Best settings for a heating boiler aquastat control:

Here we explain how to choose the best settings for a heating boiler aquastat - the combination control that sets boiler temperature and may also control hot water production via a tankless coil on the heating boiler.

We also give advice on how to set the aquastat controls if heating with a woodstove.

What Settings To Use on a Heating Boiler Aquastat Combination Control

After explaining the Hi, Lo, and Diff controls we review the newer universal replacement aquastat from Honeywell, the L7224U Universal Aquastat, followed by a discussion of the simpler single-limit control switches.

At AQUASTAT CONTROLS we explain how aquastats work, defining the functions and dials of the aquastat HI LO and DIFF control along with the reset button often found on these heating boiler controls.

This article series answers most questions about Heating System Boiler Controls on central heating systems to aid in troubleshooting, inspection, diagnosis, and repairs.

The photo above shows a the "HIGH" or "HI" setting on a Honeywell R8124A combination heating control, also called an "aquastat". Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.

[Click to enlarge any image]

The internal view of the Honeywell R8182D (left) can be found along with additional details about this control in the Honeywell R8182D,H Combination Protectorelay™ Primary Control and Aquastat® Controller Installation Instructions (link to copy below atReferences or Citations ).

Following wiring details in the instruction manual, the R8182D,H can replace other aquastat controls such as the Tradeline R8182B, R8182E, R8182F, R8182H, R8182J, or White Rogers 6C92. A newer combination control from Honeywell,

the HONEYWELL L7224U OIL ELECTRONIC AQUASTAT CONTROLLER can replace more than 40 older hydronic controls.

Lots of people, even some service technicians are confused about the actual function of combination controls and aquastats like the Honeywell R8182D. Some don't know how to set the "HI", "LO" and "DIFF" dials on a combination control.

Rule of Thumb for Setting HI LO DIFF on an Aquastat

Or more commonly, we were taught to just use a "rule of thumb" which set the

• HI to 180 °F (should be 200F or lower)
  • a HI-DIFF value is hard-wired in the R8182 series type aquastats, is not adjustable, and no control dial is provided.
    
    A programmable HI-DIFF is available on on some programmable aquastats such as
    
    the AQUASTAT L7224U UNIVERSAL and can be adjusted.
• LO to 160 °F (must be 20 below HI)
  • DIFF (or LO-DIFF) on most aquastats such works with the LO limit only and is often set to 10, or is just set randomly (not recommended - proper numbers are below) .

These were "Safe" settings for this control, and it's in with similar settings on millions of heating boilers. But with a little thought, we can adjust these HI LO DIFF settings and thus set the heating aquastat control so as to save a bit more on heating cost, and/or we can set the control to give us a bit more hot water where a tankless coil is installed.

Guide to Best Settings for the HI Limit on a Honeywell R8182D Heating Boiler Aquastat & Similar Controls:

The "HI" on a combination heating control like this aquastat is usually set by the heating service technician to a spot between 180 °F and 200 °F. Or the "rule of thumb" fellows just park it at about "180" °F as you can see in our photo.

Setting the HI: save money on heating costs by running the boiler at a higher temperature

Generally a heating boiler is more efficient if we operate it at a higher temperature.

The thermal conductivity of heating water inside of finned copper tubing baseboards or through radiator surfaces is exponentially greater at higher temperatures.

In other words, hotter water actually transfers heat into the occupied space more efficiently than cooler water.

Since this is not lab-grade equipment these settings are not precisely accurate. For this reason we like to set our HI limit at around 200 °F.

We let the boiler run through a few heating cycles, watching the temperature and pressure gauges on the boiler to see what temperature we're actually reaching. And we watch the boiler relief valve to be sure we're not causing leakage there.

Watch out: Setting the "HI" too high on the aquastat can result in over-temperature in the heating boiler and can result in dumping water and temperature and pressure at the relief valve. If your TP valve was not leaking before and it begins to drip when you set up the HI to 200 F, step the HI back to 195 and try that setting.

If your TP valve is leaking at 195 or less it's likely that you need a heating service call - something's probably wrong with the relief valve, with system operating pressures, or with the controls.

Guide to Best Settings for the "LO" Limit on a Honeywell R8182D Heating Boiler Aquastat & Similar Controls:

In our photo at left you'll see where the heating service tech left this "LO" limit control after cleaning and tuning the heating boiler.

The "LO" is set at least 20 deg F. below the "HI" limit on a combination control.

If we set the "LO" any closer top "HI" it is possible that the control, trying to give priority to making domestic hot water for someone in the shower, will simply lock out the circulator pump entirely - the heating circulator will never run.

Your heat will work, but slowly, and more expensively, as we explain next

at CIRCULATOR LOCKOUT.

We like to keep our LO set at 20 F below the HI. That keeps the LO temperature operating range as high as possible in the boiler and that in turn gives us the most heat stored in the boiler for making hot water through the tankless coil.

Avoiding Circulator Lockout - Set LO 20 or more below HI

What happens if you "cross the controls" and set "LO" above "HI" or if you set "LO" too close to "HI"? The circulator will not run.

Watch out: don't set the LO above or higher than the HI temperature limit. If you make that mistake, you will lock out the circulator pump and your heating system will not work properly. We call this "lock out" - the circulator will be locked out of running on a call for heat. Others call this LO higher than HI "crossed controls".

We've inspected homes at which the owner, for decades, observed that the heat in the building was very slow to come up in response to the thermostat. The problem was that the LO was set close to or even above the HI - the circulator pump never ran and hot heating water circulated but only very slowly by convection.

We found a home where the owner had set the "HI" to 120 and the "LO" to 180. Luckily for them, because their flow-control valve was either absent or not working, their home would indeed receive heat - but very slowly: their circulator pump had never run.

On seeing this setting we asked the owner about it. "Well you know", he said, "we have noticed that the house was always very slow to heat up in winter."

Thanks to reader L. Clark for pointing out that we had inconsistent language in this explanation. It's been fixed, and fixed again thanks to reader Damian for suggesting further clarifications.

Guide to Setting the "DIFF" (differential) on a Honeywell R8182D heating boiler aquastat & Similar Controls:

Where a tankless coil is installed on a heating boiler to make domestic hot water (for washing and bathing) we prefer to set the differential (DIFF) to its highest number (usually 25 degrees).

Our photo (left) shows the DIFF adjustment on a Honeywell aquastat. This DIFF is set to its lowest value: 10 °F.

At the setting shown, if LO were set to 120, when the burner is re-heating the boiler water and water temperature rises to 130 F the burner will turn off and the heating circulator pumps will be allowed to turn on (and they will actually turn on if the room thermostat is calling for heat).

If you re-set the DIFF dial up to its maximum of 25 and LO remained at 120 F, then when the burner is re-heating the boiler water and water temperature rises to 145 F the burner will turn off and the heating circulator pumps will be allowed to turn on (and they will actually turn on if the room thermostat is calling for heat).

In short, DIFF = 25 should give you hotter boiler temperature and thus more domestic hot water than DIFF = 10.

Still not enough hot water from your tankless coil?

First see HOT WATER IMPROVEMENTS where we discuss working with a tankless coil to get as much hot water as we can.

Then when your bath tub still doesn't have but a few inches of hot water,

see HOT WATER QUANTITY IMPROVEMENT

Watch out: be sure that a mixing valve or anti-scalding valve is installed to avoid hot water burns as well as to make effective use of this higher boiler temperature.

See ANTI SCALD VALVES & TEMPERATURE CONTROL / MIXING VALVES

For details about the HI, LO, and DIFF actually work, AQUASTAT CONTROL FUNCTIONS refer to our text and to the yellow-colored area in our colored version of the HI LO functions explained in detail

in that article's section that gives more details

about HOW THE HI AND LO LIMIT CONTROLS FUNCTION ON AN AQUASTAT above.

[Click to enlarge any image]

From that article, this quote helps explain what the DIFF control is doing on an aquastat:

When boiler temperature is rising: 

on an aquastat control, the "DIFF" or differential control dial specifies the amount above the LO or "Low Limit" to which boiler temperature must rise before the burner will turn off and the circulator will be allowed to run.

It's not hard to understand why heating service techs and homeowners are confused about LO and DIFF settings on a heating boiler, but Honeywell got it right: if we are making hot water with a tankless coil, by locking out the circulator at lower boiler temperatures, the LO and DIFF make sure that heating priority is given to the woman in the shower, not to the building radiators.

[Click to enlarge any image]

The diagram above is explained

at AQUASTAT CONTROL FUNCTIONS

Do You Want to Disable the LO and DIFF settings on a Boiler that Does Not Use a Tankless Coil for Domestic Hot Water?

If a tankless coil is not installed on a boiler where this combination aquastat control is installed, this combination control may still be in use.

And that's not always desirable. It depends. In this case, the "LO" has almost no use whatsoever and, if you read the instructions provided by the control manufacturer you'll probably see that the manufacturer calls for the "LO" to be electrically disconnected entirely.

Details about how to make this change to a typical aquastat, along with problems to watch-out for have been moved to a new article found at AQUASTAT LO & DIFF DISABLED [Live link is given just below]

Keep in mind that the LO and DIFF control settings only make sense if the heating boiler has a tankless coil installed to make domestic hot water (for washing and bathing).

If your heating system does NOT include a tankless coil, the LO and DIFF are keeping heat in the boiler for a tankless coil that is not present and you could consider either disabling this circuit entirely or setting both LO and DIFF to their lowest settings.

Details on how to turn off the LO / DIFF when you're not using a tankless coil on your boiler are at AQUASTAT LO & DIFF DISABLED - live link given just below.

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2023-03-30 by Ken - adjust aquastat to fix boiler short cycling?

I see you recommend 160 lo, 180 hi for Aquastat setting and some specific info for when there is a domestic hot water loop into a tankless coil.

Any changes you would make for a SuperStor which is on a regular Taco valve heating loop. Details are 2400 SF house, 4 zones, Beckett burner, Peerless WBV-03 112K BTU boiler, Taco SR506 switch relay.

I have had some short cycling problems this year and we are currently set to 140 lo, 180 hi. Heat is sufficient for the house (southern NH) and comes up quickly.

On 2023-03-31 by InspectApedia Editor (mod) - aquastat short cycling or "rapid-cycling" question.

@Ken,

If the boiler is short cycling let's first see which zones are calling for heat.

It could be that a circulator isn't running or not running properly so that for some heat calls the water in the boiler is heating up quite quickly.

Let me know which zones are active when you see short cycling.

On 2023-04-20 by Ken

@InspectApedia Editor , So while I was away, my service tech installed a new Residio L7224/7248.

Since there are very few heating calls now, the only zone that calls for heat is the SuperStor 40. Boiler temp was reading 179 when I last visited.

Short cycling seems to have stopped but I will write back next winter when we actually have some need for heat! Thank you!

On 2023-04-20 by InspectApedia Editor (mod) - aquastat short cycling or "rapid-cycling" fixed by new aquastat

@Anonymous, @Ken

Thank you for following-up with us on this aquastat short cycling or "rapid-cycling" question.

It's possible that the prior unit had a defective sensor but in any case your post will help other readers.

Do let us know how the replacement Residio L7224/7248 aquastat is working at your next heating season.

Daniel

On 2023-03-08 by rob - we run out of hot water at one bathroom

We have a boiler system with 4 heating zones. The water in the master bedroom shower (second floor, furthest from the boiler) never seemed to stay hot for very long.

I've set the aquastat settings in accordance with this article and it didn't seem to make any difference.

(I also adjusted the temperature setting in the Grohe shower valve.) I then noticed that if I crank up the heat in all 4 zones about a half hour prior to a shower, the hot water is fine.

Is there some other setting/valve/part I should be looking at?

(As a side note, the shower in the spare bedroom usually has sufficient hot water.) *shaking head* Thanks

On 2023-03-08 by InspectApedia Editor (mod) - not enough hot water

@rob,

First, this discussion presumes that your domestic hot water for washing and bathing is being made by a tankless coil on a heating boiler.

If some building areas have adequate hot water and others do not, then the problem is not coming from the hot water source itself, it's a different problem such as:

- the effect of an anti-scald valve or temperature setting at the fixture (like your Grohe shower valve)

- the effect of longer runs of un-insulated hot water piping between the hot water source and the fixture

When you take steps to make the boiler as hot as possible, it's got more heat to send into the tankless coil that's making hot water to be delivered to fixtures - thus surviving effects like the ones we just cited.

See details at:

TANKLESS COILS. https://inspectapedia.com/plumbing/Tankless_Coil_Guide.php

where you will find a series of articles about how to get the most hot water out of a tankless coil system.

Also read our explanation of the LO and DIFF settings above as those (along with any anti-scald devices on the sysetm) determine the hot water supply settings for a tankless coil system.

On 2023-02-11 by rick - when the water gets up to temperature the burner shuts off and the water temp drops within seconds,

@Anon, I would sure like to know what happens with your boiler. I have a similar problem: when the water gets up to temperature the burner shuts off and the water temp drops within seconds, so the burners cycle on again. I have timed some of the cycles the shortest time the boiler was off was 28 seconds. One of the longer times was over 4 minutes.

On 2023-02-11 by InspectApedia Editor

@rick,

It may be confusing but this particular Anonymous reader that you've added your comment to actually first started asking questions of us back on 2023-01-04 with many back and forth responses from us as Anon continued to ask additional and different questions.

Some of that additional discussion is just above at the start of this Comment Box section but the majority of it is in the article itself, above on this page, in the Reader Q&A section, beginning 2023-01-04 and continuing all the way through 2023-01-17.

If you read through that discussion (rather than us trying to recreate all that info off the cuff again here), you will see our suggestions for diagnosis and repair of the cycling you describe.

If you still have questions after review of that Anonymous reader exchange, please let us know.

On 2023-01-28 by Jim Hickey - need help with aquastat settings - or with bleeding air from heating system

Hi, Jim Hickey again. I wrote to you on 12/16/22. You asked for more info on aquastat. First I'd like to say Thank-You.

Wood boiler 1981 Jenson
Serial #2699
Old aquastat Honey Well
125017AAA7942
New aquastat Risideo
HWL7224U1002
Oil boiler Weil-McLain
Boil size A-B-0815
Series 3 CP0180134?
Old 1977
Don't know old aquastat ??
New aquastat relay
Type L8124A,C

I know not the best Info. Any help or direction to go, would be appreciated.

On 2023-01-28 by InspectApedia Publisher - Resideo L7224U1002/U is a Universal Electronic Oil Aquastat

@Jim Hickey,

Diagnostic might be your observation that the behavior of the boiler has changed from a "normal" or "longer" on-cycle to a much shorter and by your description very regular and unsually-brief on-cycle. So what's changed? When you get an on-site, experienced, service tech s.he will doubtless look at

- control settings
- signs of proper or improper boiler tune, combustion air, operating temperatures, cvntrols
- circulator pump operation
- adequacy of thermal contact of the aquastat's thermal sensor in the sensor well
- (less likely) thermostat wiring and operation
- any changes to control settings or wiring from prior conditions

Your Resideo L7224U1002/U is a Universal Electronic Oil Aquastat with EnviraCOM communication

That means it can be wired and set up for almost any residential heating boiler operating requirement, and it adds a feature that permits addition of an outdoor temperature sensor that adjusts what the aquastat does in an effort to improve system operating economy.

SO do let us know what the onsite service people have to say.

On 2023-01-28 by Jim Hickey - some heating pipes may need air bleeding

@InspectApedia Publisher,

Unfortunately, the tech called back and said they'd have to reset the system by bleeding the pipes to the whole house before diagnosing instead of replacing parts and that would take half a day, at $149/hr minus 25% for having the gold contract.

Does bleeding the whole house of water make any sense? I get the impression they mean actually removing all water.

I'm sorry to go over this again, but I'm confused why all baseboards and pipes are warm/hot, and when I bled the baseboards upstairs that have valves (no valves on the baseboards in the 2 downstairs rooms) only water came out. I've been told even though we have baseboards downstairs and upstairs that if there's only 1 thermostat, that it's all one zone.

However, I do occasionally hear water moving in some pipes in the unfinished ceiling that's the floor under the living room. Those pipes have blue faucets on them.

Should I be bleeding them as well? I just went down to take more pictures of the pipes at the boiler and heard some of what I'm assuming is water bubbles moving through the pipes there as well, so there still must be air, but why isn't it at the valves?

On 2023-01-28 by InspectApedia Publisher - air trapped in heating lines blocks or partly blocks hot water flow

@Anonymous, Jim Hickey

Not quite.

There can be air trapped in heating lines that blocks or partly blocks hot water flow somewhere in the loop of heating piping, yet that air may NOT find its way to bleeder valves at individual radiators or baseboards. If a tech suspects that she/he will use a more forceful method (a pony pump) to push water at enough pressure and volume through the system to get rid of any such air.

Air gets trapped at such intermediate location in building heating piping probably as a feature of the pipe horizontal run lengths and lack of slope, possibly affected by the sequence or location of elbows, valves, etc.

The fact that you SEE drain valves installed mid span in some of your piping - like in your photo - suggests that perhaps that someone has had this problem in this building before. But I do NOT advise that YOU try opening the two drain valves in your photo.

From just the photo we don't know where or what those are, and even if they're indeed on heating runs, you don't have the necessary equipment nor training and you might get scalded (burned) or might make the heating system performance even worse.

Let us know what the heating technicians do and what is the result.

On 2023-01-28 by Jim Hickey

@InspectApedia Publisher,

So it sounds like we have no choice but to either let it continue running inefficiently, or let them bleed the entire system's pipes, which they say will take half a day? Why would it take that long? This is baseboards, not radiant floor heating that I assume would have a lot more piping.

I think you'd suggested the check the system for overfiring? I found and read an article that also maybe indicates a possibility of the oil pressure being off. Shouldn't they be checked first? https://www [dot] achrnews [dot] com/articles/91933-btu-buddy-11-handling-an-over-fired-boiler

On 2023-01-28 by InspectApedia Publisher

@Anonymous,

Sorry, but no, I've exhausted this topic. I've outlined and we've been over every situation suggested by your comments, questions, and discussion - for which we thank you.

In my OPINION it's past time to - that is now quite overdue - to pay for an onsite heating professional.

Do let us know what the service manager and service technician ultimately say and do - as that might help other readers.

On 2023-02-08 by Jim Hickey

@InspectApedia Publisher,
I was able to get the tech service manager here. There was air trapped in the system, forcing most of the water to recirculate right in the loop at the boiler, even though all "fin-tube convector" valves we could get to only let water out.

Doing research, I realized that what I was calling baseboards was an incorrect term. He checked all zones/equipment including the nozzle, and after getting the air out, said everything is working as it should, and the nozzle size is good for this system, though the one year it was different was not proper.

He then came upstairs and checked the thermostat. As soon as he saw it, he said that's part of the problem. Apparently, even though the Lux 9100uc TT said it could do boilers, it can't do radiant boilers.

We now have a Honeywell T6 pro. Unfortunately, it's been warmer a couple days and expected to be a few days more, so it'll be awhile before I can get a good test of the system.

On 2023-02-08 by InspectApedia Publisher - service tech confirms our early diagnosis

@Anonymous,

Thank you for taking time to update us and other readers on diagnosing this heating problem.

Back in January at my initial response I suggested the air-bound heating system problem.

This is a good reminder for us both of the difficulty of trying to diagnose technical issues remotely where all we have is text.

We're so glad that your system is working again.

I think a lesson for me here is to suggest, still ore emphatically, when it's time to get a trained, experienced technician on-site.

On 2023-02-09 by Jim Hickey

@InspectApedia Publisher,
Well, as the service manager requested, I did not program the thermostat yet so that I could turn it up when I got up and pay attention to it. After the first time on in the morning, it's still doing 4 minutes on and 8 minutes off, but at least it reached setpoint faster.

On the other hand, it's not very cold outside. I reached out to the service manager again and he said that's normal, that it's keeping the water at a good temp to heat the house.

On 2023-02-09 by InspectApedia Publisher - air bound heating systems

@Anonymous,

Thanks for the update.

Indeed it's normal for a hydronic (forced hot water) heating system to cycle on and off and for the circulator to cycle as well, though a precise, exact to the second cycling interval is a bit unusual.

Keep in mind that even after air has been bled from a system (in this case they may have had to use a forceful method to do that), if there is an air leak into the system or a water leak out of it, the air blockage problem will return.

You should read

AIR-BOUND HEATING SYSTEMS

Our discussion may fit better on that page than on this one of optimum HI LO DIFF settings for aquastats.

On 2023-01-25 by Anon - still have issues with boiler short cycling

Hi, follow-up to the conversation about our boiler running 4 minutes then off for 8 minutes repeatedly. I had an appointment for today but the tech called and asked what the problem was. He says that's the way the boiler is supposed to to work, to avoid overheating, but agrees it shouldn't take hours to come up to temp.

I was told the service manager was going to be coming but now he's not available. He's going to try to get in touch with the service manager and I'm not sure if anyone is still coming to day or not From what understand from this conversation, this is not the way t should work and until several years ago, it was fine.

It could come from 62-68 by the time I set the thermostat for, with the early recovery mode. Now it can't do 64-66 in less than a few hours. Suggestions, ideas?

On 2023-01-25 by InspectApedia Publisher

@Anon,

Sorry, but no, I've exhausted this topic. I've outlined every situation suggested by your earlier comments, questions, and discussion - thank you.

Do let us know what the service manager ultimately says - as that might help other readers.

On 2023-01-05 by InspectApedia Publisher - boiler is running a lot with twin Thermo Disc 59Ts

@JC,

For a conventional aquastat like the Honeywell described above on this page, I'd use the optimal settings given above on this page - usually.

In Toronto the heating people often set up a boiler so that the circulator runs continuously and the thermostat (the one that calls for heat in the occupied space) will simply turn the boiler on when it wants heat.

The 2nd thermostat for your hot water will run the circ that runs boiler water through the coil to re-heat the indirect hot water tank.

Now about the Thermo-Disc-59T - that's normally used as an electric water heater hot water control - you can see its settings - factory- in the photo.

A Therm-O-Disc 59T 4300 66T 4401 Surface Mount Thermostat Limit 120 to 180 F, 120V like that shown below has its operation given in this nice summary

THERM-O-DISC-59T-66T-CONTROL [PDF]

On 2023-01-05 by JC

Hi folks. Hope everyone's warm. I have a question an hope some details may help:

I have a nice cast iron OLSEN OSC-4 burning nat gas with the original TACO pushing through all iron rads via a single zone valve. 1500 ft of home, roughly, with decent insulation and windows, so sized right.

Off to the side of the OLSEN, there's a separate loop to an old AERO A-50 storage tank.

All from 1999 and still running strong.

The AERO tank is fitted with its own TACO circulator which runs the tank water through a single-walled sidecar exchanger nestled into the side of the ext tank skin - no internal loop in this AERO - and so the boiler TACO pushes one way, while the tank TACO pushes the other. Voila, hot water in the storage tank.

Priority for the full kit is DHW. Eg if the AERO still wants DHW heat, we get no space heating.

On the AERO are two Therm-O-Disc 59T stats that run back to a control module bolted to the OLSEN boiler. Installer labelled 59T#1 as "boiler" 59T#2 as "pump". I reckon this means #1 calls for the boiler to fire and circulate while #2 runs the other (dedicated) circ for the heat exchanger. All guesses but it kinda makes sense to me.

Assuming this to be mostly true, what should these be set at? Same preferred temp, near enough? One high, one low?

I get the sense that the boiler is running A LOT these days, being called by the tank trying to heat that tank water, and the boiler bumps up against its own high limit, then cycles again after it cools some.

I've tweaked the 59Ts in the past and suffered from a "lock out" of some kind, then re-tweaked one or both of them until the zone valve opens for the rads and all is good. No clue how I messed it up, no clue how I "fixed" it. Just me twiddling slotted dials.

Yet there must be more logic to it versus grabbing a screwdriver and turning the dials.

What's the best practice I should follow here in terms of setting up the twin 59Ts?

We live in the Golden Armpit/Toronto, with -10*C winters not uncommon.

We like ~130* water at the tap and this system delivers unless all the laundry, showers and kitchen are hauling hot water, then it wobbles for a half hour or so (but this doesn't concern me).

- Sidecar heat exchanger stripped and cleaned a few years ago, all good.
- Tank TACO replaced at the same time, all good.
- High Limit on the OLSEN is 180*:
- WATTS tank replaced a few years ago, working great, all good.
- System rests at 12-14 lb
- System runs at 22-26 lb
- T&P on the OLSEN is clean, no drips
- Flue gas analytics shows she still burns clean.

Any ideas on optimizing those two 59Ts or otherwise fine-tuning this rig?

Thanks and Happy New Year.
JC
Toronto, ON

On 2023-01-05 by InspectApedia Publisher - why is boiler short cycling

@JC,

Sense, yes but keep in mind that a common issue with any heating or hot water control device that depends on contact with an exterior surface like that of a pipe or tank is that its behaviour can become erratic or flat wrong when any of several factors affect the quality of the contact between its sensor surface and the hot water pipe or tank surface:

• it has to be tight
• the surface of the pipe or tank has to be clean
• the surface of the sensor has to be clean
• the location of the sensing point might also be relevant
  

For example, if nothing else has changed but your system isn't working as it used-to, I'd consider removing the two sensor controls and cleaning up everything, then re-installing them.

On 2023-01-05 by JC

@InspectApedia Publisher, cheers for your reply.

Nope, no continuous-run TACO circ on the boiler. Not set up that way. When nothing calls for heat, nothing runs: either full on or full off.

I think my Q is more about setting the twin 59Ts on the indirect AERO. If one of those calls on the boiler to circ + fire (main loop), while the other runs the heat exchanger circ (tank loop), should they be set at approx the SAME TEMP? Should the heat exchanger circ stir up the tank a little before the other stat calls the boiler?

** And thanks for the schematic and info on the 59T you attached. Mine are older than that, but the point's the same. What that info told me is these stats "sense the surface temperature of the water heater TANK..." eg not the water inside the tank, but the jug that holds it.

Which may answer that part of my question as to the apparent short cycling: these stats are inside an ACCESS PANEL the cover of which was lost long ago. So they sit open. Makes it easy to adjust sure, but if they are sensing the TANK surface temp they're probably quickly cooling to the ambient air and fooling the boiler into firing more often.

Of course, the WATER in the tank is pretty hot and the stat is satisfied pretty quickly, ergo, short-cycling. **Does that make any sense to you? I'm gonna search for that access cover or jury-rig something to see if the behaviour changes meanwhile.

Thanks for your thoughts again.
JC

On 2023-01-05 by JC

@InspectApedia Publisher, I'll try the low-hanging fruit first and carve some pink foamboard to fit the access cavity in lieu of the lost cover, ... give the 59Ts a warm dark cave to sit in, un-exposed to drafts etc - see if that makes them happier ... cheers, JC

On 2023-01-05 by InspectApedia Editor

@JC,

I appreciate the sense of trying to insulate near temperature sensitive control, but if this is a new problem and the installation hasn't changed and I don't think that that's the issue. Also I'm a little nervous about the fire safety of putting combustible foam insulation around and up close on an electrical device.

On 2023-01-05 by JC

@InspectApedia Editor , understood, yet the stats were surrounded by yellow batt, then a steel cover (until i foolishly lost that cover... ) so someone thought these could be enclosed by design i guess... we're not talking mains voltage or any kind of current here, 24V off the transformer ... and beyond losing that cover, nothing else has changed no, just that it seems to be short cycling;

i didn't even think that these were a kind of hard surface stat and not immersed in some fashion - never crossed my mind ...

On 2023-01-06 by InspectApedia Publisher

@JC,

There is both line voltage (120VAC) and also lower voltage inside the aquastat.

On 2023-01-06 by JC

@InspectApedia Publisher, thanks but this is all 24Volt running through the 59Ts on 18 ga. wire, stepped down by transformers bolted near the boiler motherboard. (Ignore the AERO rating plate in the picture).

When the stats close across TV-T the mains throw for pumps & the blower happens back in the relay box (R8222C).

On 2023-01-06 by InspectApedia Publisher - why a temperature sensor on a hot water tank would turn on a circulator is clear

@JC,

Thank you for the added detail. It's another example of the difficulty we face in trying to be helpful in discussing heating controls when we have so little information about an actual installation. Even now I don't have a complete, clear picture of your installation.

The phrase

When the stats close across TV-T the mains throw for pumps & the blower happens back in the relay box (R8222C).

leaves me uncertain about what components make up your system and what is being controlled. Why a temperature sensor on a hot water tank would turn on a circulator is clear: to re-heat water in an indirect-fired domestic hot water tank, by turning on a circulator pump that circulates heating boiler through a coil that in turn heats hot water in the hot water tank.

But what "blower" is where and what you mean by "blower happens" and what "relay box" we're discussing is, apologies, unclear. Maybe a sketch of the system and its components would help.

On 2023-01-15 by Anonymous - trouble with LUX 9100U control

@InspectApedia Publisher,

This conversation actually started on Jan 4. When it was moved to here to aquastat, I started a new comment/question. Al info seems to be above in this chat.

We're now wondering why the Lux 9100u thermostat sends and electrical signal to the burner when I'm only touching a button once to turn the backlight on. It takes 2 pushes to change anything.

On 2023-01-16 by InspectApedia Publisher - temperature swing vs burner cycles per hour

@Anonymous,

We often have a bit of a struggle deciding where to keep conversations on pages that are on-topic. The relevant data and possibility of helpful observations from other readers work best if we try to keep topics and pages together.

You probably have the LUX9100U THERMOSTAT MANUAL [PDF] Lux Products, originaL source: https://www.luxproducts.com/wp-content/uploads/2017/07/tx9100u_manual_en.pdf.

I don't see any discussion from Lux that approaches your question of when the TT is signaling the boiler. For sure, you'd think that just touching to wake up a display ought not "do" anything else.

BTW there are some dip switch setting recommendations in the manual that you might compare with those on your thermostat.

Do take a look at their discussion of the Swing Setting starting on p. 23:

TEMPERATURE SWING AND OFFSET SETTING: A thermostat works by turning your heating or cooling system on and off whenever the room temperature varies from the desired set-point temperature.

The amount of this variation is called the swing. Generally your system should cycle on about 3 to 6 times per hour. A smaller swing number makes the system cycle more frequently, so the room temperature is more precise and constant.

A larger swing number will make the system remain on for a longer duration each time and decreases the number of cycles per hour. There is only one Swing setting, and this determines the cut-in and cut-out points for both the first and second stages (if present), in both Heat mode and Cool mode.

On 2023-01-16 by Anon

@InspectApedia Publisher,

Ok, I've changed that setting already. Thank you again. Heat is already set lower for the night, so I will check back tomorrow.

I do wonder if the thermostat is malfunctioning somehow as well as whatever the other issue is, since the instructions say to hit any button to turn on the backlight. Earlier when the set temp and room temp were the same, it clicked and flashed the set temp 3 times then "heat" 3 times then the boiler came on.

However, after being near the thermostat checking settings, and the detected temp raising above set because I was near, I tried again out of curiosity to see if that would happen again and it didn't.

I'll experiment with that again tomorrow as well, but I doubt it's a coincidence.

On 2023-01-16 by InspectApedia Publisher

@Anonymous,

Nah; your questions, even when frustrating for us, help us understand where we need to provide more or more clear information.

About your thermostat

Delay time: 2. default is 5 but I was trying to force it to run more often to get it up to temperature.

Try setting that back to 5 and see what happens.

On 2023-01-16 by Anonymous - TX9100uc heater settings on our L7224& Aquastat

@InspectApedia Publisher,

I also apologize for how frustrating it must be for you to work with someone who knows nothing about these systems.

When you mentioned the dipswitches, I realized that I typo'd when mentioning which model I have, which is actually the TX9100uc https://www.luxproducts.com/wp-content/uploads/2017/07/tx9100uc_manual_en.pdf

This model has all the settings accessed through programming, and my settings include:
Early recovery: on
System mode: furn
Fan: gas (what directions say for a boiler)
Delay time: 2. default is 5 but I was trying to force it to run more often to get it up to temperature.
Temperature swing is set at 1 (range 1-9 with 1 being smallest) Trying to force t to keep temp once it got it.
Offset: 0 because a boiler doesn't have second stage heat. (default 2, range 1-9)

As far as the backlight apparently sending a signal to the boiler, the manual says: The display screen is lighted to assist viewing at nighttime, or in locations with low light levels. A press of any button on the front panel will light the display for approximately 10 seconds.

The L7224U aquastat settings:
HL_ is set at 190 (was 180)
Hdf is set at 10
LL_ is off
duu is off
ASC is set at 0 sec
tPL is off
PC- is on

Do all these settings look good to you?

Last night I changed the delay back to 5 as suggested, and this morning I see it makes no difference. The boiler is still doing the 4on/8off sequence.

On 2023-01-16 by InspectApedia Publisher - checking the firing rate of the oil burner

@Anonymous,

About the changing the delay back to 5 - making no difference, that's a helpful diagnostic step. So we're back to checking the firing rate of the oil burner.

On 2023-01-16 by Anonymous

@InspectApedia Publisher,

I was just looking back at the service records I got from my provider and it looks like they've always used a 75-80B nozzle (no brand listed) but one year they used a 60-80A Delavan.

I'm trying to decipher the info here about nozzles. Are these 2 nozzles interchangeable or if not, which is the proper size? The boiler is a Beckett RSA85LN-TB. It appears the oil filter has always be #3.

On 2023-01-17 by InspectApedia Publisher - Oil burner nozzle spray patterns and delivery rate

@Anonymous,

Please use our on page search Box and search for the phrase

Oil burner nozzle

And you will see we have articles explaining about spray patterns and angles and delivery rate in gallons per hour. That will be more accurate and thorough than if I try to make that up de novo here off the cuff.

On 2023-01-17 by Anonymous - boiler firing range on burner label?

@InspectApedia Publisher
I went down and found that label. The way I understand the info online, since the label does not show a "firing range" but does show 2 nozzle sizes, does that mean the year a 60-80A was installed, it was not a correct one for this burner?

On 2023-01-17 by InspectApedia Publisher

@Anonymous,

No it means that the technician has, if you are correct in the number you give is actually the nozzle that's actually installed, downfired the boiler which would be in response too and overfired boiler in the 1st place. Now it's time too get actual data on what's actually installed.

Ask your tech to check the firing rate - the nozzle size in gph Of the nozzle that is actually on the burner.

And then ask the technician to investigate what you have described as a too short and too frequent burner on cycle.

Please report back to us what you are told when you have done that.

You need a heating service call at your home, by an experienced service technician.

Do let us know what you're told - what she or he finds - as that will help other readers who've slogged through this problem.

On 2023-01-17 by Anonymous

@InspectApedia Publisher,

Thank you for all your help. That's what I was afraid it would come down to.

On 2023-01-17 by Anonymous - how do I find out the right firing rate for my boiler?

@InspectApedia Publisher,

I assume the firing rate isn't something they can tell me via email or phone and it's at the point where we have no option but to set up at service call? They charge $149/hour and I don't understand why it's not covered by my "gold contract". I believe it had been in the past.

I believe I've read all articles suggested. We know it has been taking hours to come up to set temp for years now. I t may have coincided with changing the thermostat or it may coincide with having the aquastat replaced. We're not sure.

On 2023-01-15 by InspectApedia Publisher

@Anonymous,

Keep in mind that I'm quite limited in what I can see of your system from here .

Seems as if the next thing to do is ask your tech to check the firing rate - the nozzle size in gph.

On 2023-01-15 by Anonymous

@InspectApedia Publisher,

Yes, I am in the US.

What we're trying to figure out is why the boiler comes on for 4 minutes, reaches it's HI limit and goes off for 8 minutes, repeatedly until the room is at set temp which is often many hours.

I have observed that the 8 minutes is all it takes for the boiler temp to cool off 10-11 degrees to get below the Hi temp differential so it can come back on. The circulator pumps seem to be working.

We've also just discovered there may be an issue with the thermostat at well.

On 2023-01-15 by InspectApedia Publisher

@Anonymous,

Yes we understand that that's the question; we've suggested several things to check, including both settings (which you are confident are correct) and over-firing - something that your heating tech can examine.

It may also be diagnostic to consider when this boiler on-4 off-8 minute cycle first occurred. Since new installation, since work was done on the boiler, or since something else changed?

If you're in the U.S. and your heat is controlled as typical,

The articles in this series explain how the aquastat turns the boiler on or off in response to temperature:

The thermostat, on a call for heat, turns on the circulator for that zone.

The aquastat, in response to the temperature in the boiler, will turn on the burner when needed.

On 2023-01-15 by Anon

@InspectApedia Publisher,

I was previously told that the LO limit that is off in the settings the technician set is the way it should be since there is no tankless coil . The Hi Limit differential is set at 10 and I was told that is correct as well.

Further observations as I’ve been listening to the boiler all day:

Twice now, when I haven’t heard the boiler come on in half an hour or more, at about 40 minutes and at about 35 minutes I touched the thermostat to make the light come on so I could see if the room temp was the same as the set temp.

Both times, room temp was at 68 and the set temp of 68 flashed a few times and the word “heat” flashed a few times. Maybe 10 seconds later, the boiler came on.

I’m beginning to think we have 2 separate issues because it doesn’t seem like the thermostat issue (if there is one) can explain why the boiler has the 4 minutes on/8 minutes off Hi limit issue.

As far as the HI limit, if the boiler temp goes below differential does the boiler come on long enough to check the thermostat to see if heat is being called for. If not, does the boiler temp continue dropping until the thermostat calls for heat again, when the room temp has gone below the set temp?

I hope this make sense to you because I don’t know how better to put it into words.

On 2023-01-15 by InspectApedia Publisher

@Anon,

Typically the HI differential is built into the control, and the DIFF dial has to do with the LO setting.

But as the control comes from the factory, unless the LO has been actually disabled (we have an article on how to do that), it's at work.

So if the LO is set at than 20 degrees or more below the HI you have locked out the circulator and your heat rising into the building will be terribly slow.

On 2023-01-15 by Anon

@InspectApedia Publisher,
I’m sorry, thought I’d said I the earlier part of the conversation that it was the boiler is oil-burning. Is there a way to connect this conversation and that one?

I’d previously read the aquastat HI/LO info and raised the HI from 180 to 190 but over the last several days it hasn’t seemed to make a difference. HI differential is still set at 10. You’d said previously that the LO limit is not needed since this is a heat-only source, since we have a separate household hot water heater.

Realistically, when the thermostat is still calling for heat, how long should it take the boiler temp to drop 10-11 degrees according to the aquastat? The gauge shows a drop of about 7 degrees and 8 lb pressure. The room temp downstairs according to a cheap thermometer is about 64 degrees currently.

While I’ve been watching again this morning, it has started taking longer between, now that the thermostat is reading the set temperature. Unless I missed hearing a cycle the boiler didn’t come on again for almost 40 minutes, though it may have been triggered by my touching the thermostat to get the light to come on so I could see if it’s still at the set temp of 68, since it was only on a minute or 2. Current temp outdoors is about 37.

I’m reading though the intermittent circulator info, but unless I’m misunderstanding, it doesn’t seem to apply to this situation. All the pipes I can get to, even well away from the boiler, are hot except what appears to be the main water intake.

As far as the sensor, looking at the info, that doesn’t appear to be anything we can access. We’re not comfortable trying to remove the aquastat, which is what it looks like the diagram is indicating.

On 2023-01-15 by InspectApedia Publisher - Causes for Hydronic (hot water) heating boiler rapid on-off cycling of the burner

@Anon,

Causes for Hydronic (hot water) heating boiler rapid on-off cycling of the burner

OK. So if the circulators are on the return side of the loop, and the pipe coming into the circulator is hot not just right at the circulator but several feet away from the boiler then hot water is circulating through the system.

When a heating boiler is cycling on and off to frequently but we are certain that hot water is running properly through the piping and radiating devices, then there are other things to check including

CIRCULATOR PUMP RUNS INTERMITTENTLY

- be sure to step through the diagnostic suggestions in this article as some of them could explain what you are experiencing.

AQUASTAT HI LO DIFF SETTINGS - above on this page

AQUASTAT SENSOR PROBE HEAT CONDUCTING COMPOUND

Watch the boiler temperature and pressure gauge when the boiler runs.

If its aquastat and aquastat sensor are working normally, when the boiler turns OFF the water temperature will be close to the HI setting on the aquastat and when the boiler turns back on, depending on the aquastat model, the water temperature will be 10-15 degrees below the HI.

You didn't give the fuel for this boiler. If it's heating oil and if the boiler is over-fired (oil burner nozzle size in gph or oil pressure too high) that could also cause the boiler to "get ahead" of the building's heating piping: water in the boiler heats up very rapidly and then is exhausted quickly by the circulator.

Let me know what you find.

On 2023-01-15 by Anon

@InspectApedia Publisher, The pipes on both sides of both circulators are hot. I also feel them and the pipes connected to them vibrating even after boiler turns off.

On 2023-01-15 by InspectApedia Publisher - are circulators running

@Anonymous,

Check that the circulator(s) is(are) running.

On 2023-01-15 by Anonymous

I've read the information in the provided links and have turned the valves on all the baseboards and water immediately came out- no air. There is only 1 thermostat in the house though there are baseboards in the basement as well as in the single level house. The basement baseboards do not have bleeder valves nor do all of the ones upstairs.

A few days ago I set the HI limit at 190 instead of 180 but except for when the thermostat first calls for heat in the morning, the boiler still runs 4 minutes on and 8 minutes off repeatedly and takes hours for the thermostat to reach the set temp that's only 2 degrees higher than night on most days.

Obviously, it takes even longer on colder days. The pipes on both sides of both circulators are hot when boiler is running.

Any more ideas?

On 2023-01-06 by Anon

@InspectApedia Publisher, Sorry, still trying to absorb all that info

On 2023-01-06 by InspectApedia Publisher - is my baseboard system airbound

@Anon,

PLEASE READ AIR-BOUND HEATING SYSTEMS - home

as that will be more complete than having me try to re-create all of that guidance here, off-the cuff. Let me know if anything you read seems unclear.

On 2023-01-06 by Anon

@InspectApedia Publisher,

The baseboard are al warm, but not what I would all hot. I had understood, based on info I had found elsewhere that each baseboard had to be bled but the service person didn't agree. Not all of them have bleeder valves, and none of the ones in the basement seem to, but I'll check the rest of them, Should they be done in a certain order? Thank you

On 2023-01-06 by InspectApedia Publisher

@Anon,

These gauges are not precise lab instruments and certainly there can be an error. If the heating system is working the way you need, then there is no reason to change anything.

What it means is that there was no air at that baseboard.

It does NOT mean that there is no air anywhere in the system and while it reduces the chances it does not mean that there is no chance that there's not an air bound line elsewhere.

But IF ALL of the baseboards are hot then the system isn't airbound.

On 2023-01-06 by Anonymous

When the service tech was last out here for the tune-up, I got him to look at the baseboard heater furthest from the boiler and said since water comes out there's no air. Does that sound right to you?

I'm still reading up on the info you sent but am wondering if the gauge reading about 172 at shutoff when the aquastat reads 180 is an issue? If yes, can it be fixed?

On 2023-01-06 by InspectApedia Publisher

@Anonymous,

The low limit on the aquastat should be off as you don't have a tankless coil for your hot water.

About the temp not coming up quickly - that sure looks as if either a circulator isn't running OR a heating line is air bound.

Search InspectApedia for AIR BOUND HEATING SYSTEMS to understand that problem.

On 2023-01-06 by Anonymous

Thank you, I appreciate the help. I know how busy you must be and you still find time to help on this board

Is it odd that the lower limit on the aquastat was turned completely off? The boiler temp was at 70 when we looked at it this morning and when it first came on awhile later for the day setting, it had to come up 110 degrees before it turned off at the high limit of 180. It took maybe 15-20 minutes.

It was only at Christmastime this year during sub-zero temps when factoring in wind chill (very unusual here) and the heat didn’t come up even 2 degrees after literally all day, that I started timing it and saw it runs 4 minutes and off 8 before coming back on again for only 4. This morning was the first time I noticed it was on much longer when first on in the morning.

On 2023-01-05 by InspectApedia Editor

@Anon,

Those are reasonable settings

On 2023-01-05 by Anon

Does the transformer look normal to you?

Any thoughts on why the gauge at about 172 doesn't agree with the aquastat at 180 or how to fix that?

It looks like the other settings I tried posting didn't actually post. Do these look right?

HL_ is set at 180
Hdf is set at 10
LL_ is off
duu is off
ASC is set at 0 sec
tPL is off
PC- is on

According to the manual, there should be more settings but this is all it shows me when cycling through.

As far as the Lux 9100uc thermostat, I have the temperature setting at 64 for night and 66 for day. I used to let it go lower at night but for years now I don't set it higher when I'm the only one home (and use a small electric heater) because oil costs so much, the last couple years, especially this year. I believe these problems started when we replaced the old thermostat because it stopped holding it's programming, or it just occurred to me that it may coincide with the aquastat being replaced.

There are other settings I've tried changing to try to make the boiler keep heat at set temp or even reach it, but they don't seem to make a difference and it still takes hours to come up even one degree. It was only this year that I started timing it and see it runs 4 minutes and off 8 before coming back on again for only 4. This morning was the first time I noticed it on much longer when first on in the morning which seem to me to coincide with your idea that the high and low settings may be off.

Delay time is set at 2 with default being 5.
Temperature swing is set at 1 (range 1-9 with 1 being smallest)
Offset is a 0 because a boiler doesn't have second stage heat.(default 2, range 1-9)

I also realize that a high pitched noise when the boiler first came on is gone. I'm not sure if that's good or bad, but I believe it was there least year as well, maybe longer.

On 2023-01-05 by InspectApedia Publisher - what are reasonable aquastat settings

@Anon,

thanks for the photo - yes indeed, this (now abandoned) aquastat had a short or arc that ruined the control board - it's quite sooty.

Thanks - that's the low voltage transformer that converts 120VAC to 24VAC for use on the control board.

You can read about this aquastat and its settings at

HONEYWELL L7224U UNIVERSAL AQUASTAT

where we discuss the optimal settings for the L7224U control.

Please take a look and let me know if you have more questions.

On 2023-01-05 by Anonymous

Here's a picture of the current aquastat, taken before the boiler came on for the morning, so it still shows temp at 70.

I do notice that the gauge says about 172 while the aquastat says 180.

And here's a close-up of the yellow block in the current aquastat.

I also noticed an old aquastat on the floor near the boiler and the yellow block in the upper right looks melted. Obviously that had been replaced at some point.

... ...

Hubby was able to help me this morning before work and the aquastat was at 70 and the thermostat showed temp at 66, the temp it's set to for morning (it was relatively warm yesterday and apparently overnight).

When the boiler first came on at the set morning time of 7:30, the house temp and thermostat were still set for 66, so I'm not sure why it came on at all. It ran for quite awhile and I took a picture of the gauge when the boiler turned off. The aquastat said 180.

I then turned the heat up to 68 to force the boiler to come on again and when it came on a couple minutes later, the aquastat said 168. It again shut off at 180 and the gauge picture was identical to the first I took.

I looked all around again and finally found the gauge below the grey box on the black part behins it. This is after not running for awhile because we set the heat lower for night. I'll try to catch a picture of it tomorrow as it shuts off.

On 2023-01-05 by InspectApedia Publisher - what does boiler pressure./temperature gauge look like

@Anon,

The boiler pressure./temperature gauge is a round dial with numbers on it - I think I see yours peeking out from under the aquastat (gray box)

See GAUGES, HYDRONIC BOILER

to understand what these look like and where they may be found

On 2023-01-05 by Anon

You had asked for a picture of the boiler settings as well but I don't know where the gauge is. I don't see it. Would it be behind another panel?

We really appreciate the help

On 2023-01-05 by InspectApedia Publisher

@Anon,

you don't set boiler pressure directly. The boiler pressure is set at 12 psi by the water feed/pressure reducer valve when it's set up. The boiler pressure gauge should read just under 30 psi at its hottest (under about 200F on the gauge)

The aquastat settings are given in the article I recommended.

On 2023-01-05 by Anon

My husband will open that box up after work tomorrow. How do we access the boiler temperature and pressure settings?

On 2023-01-05 by InspectApedia Publisher - where do I find the aquastat

@Anonymous,

That gray box with red square in center is probably the aquastat; there may be a small screw at each end that needs to be loosened.

see AQUASTAT HI LO DIFF SETTINGS

On 2023-01-05 by Anonymous

How do l get to the aquastat? Sorry, I know nothing about this

On 2023-01-05 by InspectApedia Publisher - one thermostat means one zone

@Anon,

If there's just one thermostat it's all really one zone. And one circulator.

Those Taco circulators are so quiet that it can be difficult to know if the circ is running, that's why I feel the pipes on both sides of the circ and between the circ and the boiler - assuming it's on the return side. If the pipes are fully hot then it's running.

If not, it's not. And that could explain why on a call for heat the boiler would heat up to its HI and shut off.

Next
Look at the boiler temperature and pressure when the boiler is shutting off

and

Post a photo of the Aquastat with its cover off so I can see the settings

Watch out: DO NOT touch any electrical terminals - you could get shocked or killed.

On 2023-01-05 by Anon

Thank you! It's oil fired Beckett RSA85LN-TB low pressure boiler with Beckett by Honeywell R7184B Interrupted Ignition Oil Primary Control, Beckett Electronic Oil Burner ignitor 746001, Beckett 21805 burner mode; K37MYBKN-597, Taco Cartridge Circulator model 007-F5.

Thermostat is a Lux 9100 that replaced an older Honeywell when it stopped holding it's programming, even with new batteries. I've played with the setting s on that a bit but it doesn't help.

I believe it's 2 zones, one in the basement where it is, and another for the main house. I believe they're both on the same thermostat.

On 2023-01-05 by InspectApedia Publisher

@Anon,

Let me see the boiler and its controls and the Aquastat settings

you can post one photo per comment

On 2023-01-05 by InspectApedia Publisher

@Anon,

What's the fuel: Oil or gas?

Multiple zones or one zone?
How are zones controlled?
What thermostats are calling for heat?
Have you checked that the circulator(s) are all running? (Do pipes feel hot on BOTH sides of each circulator?)

I'm trying to help and not charging you $150. hour (and you may end up needing to go that route) but first let's see if we can figure out enough details and you give enough feedback that this discussion will help other readers.

On 2023-01-05 by Anon

This boiler system is only heat. The baseboards produce heat. We get a tune-up every year and the service company is saying even with their 22-point check, they don't always notice all problems. They say I have to pay $149/hour to have them come back and diagnose it even though I've told them the system takes hours to come up in past years.

The "gold plan" offers a discount on parts and labor but I've told them in the past this takes forever to come up to temperature and doesn't run till it is. This is the first time it occurred to me to time it.

On 2023-01-04 by Anon - boiler short cycling for 4 minutes on

Does anyone know why an oil-fired boiler baseboard heat system would only run for 4 minutes then go off for 8 minutes, then back on for only 4 minutes, repeatedly, even when set temperature on the digital thermostat has not been reached?

On 2023-01-04 by InspectApedia Publisher - oil-fired boiler baseboard heat system cycling

@Anon,

There are a couple of causes of heater cycling:

1. the boiler is getting up to its shut-off temperature in just 4 minutes - which might mean that a circulator isn't pushing hot water around the heating zones very fast or not at all

2. there could be another user of boiler heat such as hot water being produced by a tankless coil

 

...

Continue reading at AQUASTAT LO & DIFF DISABLED or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see AQUASTAT HI LO DIFF SETTINGS FAQs - questions & answers posted originally at the end of this page.

Or see these

Recommended Articles

• AQUASTAT CONTROLS - home
  • AQUASTAT HI LO DIFF SETTINGS
  • AQUASTAT LO & DIFF DISABLED
  • AQUASTAT L4006, L4006E, L4007 HONEYWELL GUIDE
  • AQUASTAT L4080B,D & L8080A HONEYWELL MANUAL
  • AQUASTAT L4080B,D,F,G & L8080A HONEYWELL MANUAL
  • AQUASTAT L6006A HONEYWELL GUIDE
  • AQUASTAT L7224U UNIVERSAL OPERATION & ERROR CODES
  • AQUASTAT L7224U UNIVERSAL DIAGNOSIS
  • AQUASTAT L8124 AQUASTAT INSTALL / REPAIR
  • AQUASTAT L8148 AQUASTAT INSTALLATION
  • AQUASTAT L8148 HONEYWELL DIAGNOSIS & REPAIR
  • AQUASTAT R8182-SERIES CONTROL
  • AQUASTAT RESET BUTTON
  • AQUASTAT SENSOR PROBE HEAT CONDUCTING COMPOUND
  • AQUASTAT SENSOR PROBE STUCK in the AQUASTAT WELL
  • AQUASTAT SETTINGS vs HEATING COST
  • AQUASTAT SELECTION GUIDE
  • OUTDOOR RESET MODULE AQUASTAT ADJUSTER
  • REMOTE THERMOSTAT CONTROLS for HVAC
  • TANKLESS COIL HOT WATER HEATER TEMPERATURE CONTROL
• HOT WATER IMPROVEMENTS using a tankless coil and additional controls to get as much hot water as we can.
• MANUALS for HEATING & A/C SYSTEM CONTROLS
• SINGLE FUNCTION LIMIT SWITCH

Suggested citation for this web page

AQUASTAT HI LO DIFF SETTINGS at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to HEATING BOILERS

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