Q&A on how to choose the settings for a heating boiler aquastat control:

This article series explains 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.

Questions & Answers About Settings on a Heating Boiler Aquastat

These questions & answers were posted originally

at AQUASTAT HI LO DIFF SETTINGS - please be sure you review the advice given there.

Article Contents

• AQUASTAT SETTING ERROR FAQs - LO set to a higher temperature than HI - circulator lockout
• RESIDEO / HONEYWELL L7224U1002/U UNIVERSAL BOILER AQUASTAT DIAGNOSIS FAQs
• THERMO-DISC TEMPERATURE CONTROL FAQs

Also see our index to all aquastat control setting questions and answers at AQUASTAT HI LO DIFF SETTINGS FAQs

Also see our index to all boiler aquastat questions and answers at AQUASTAT DIAGNOSTIC FAQs INDEX

...

Aquastat Setting Error FAQs

I think my aquastat is not set correctly: High is 180 and the low is 200

I just bought a home with a 20 year old Thermo Dynamics Boiler. Former homeowner said he had a technician change the Aquastat in July.

Tried to heat the home and failed today. It is a problem with the Aquastat he installed just three months ago.

For some reason when the temp differential is set to 20 degrees High above low the system doesn't function.

It shuts itself off. The tech manually adjusted the differential so the High is 180 and the low is 200 and the house heats up now.

What is the issue with the Aquastat? Theoretically this means they're crossed, and the system shouldn't function. On 2022-10-04 by Clare Martinez -

Reply by InspectApedia-911 (mod) - Your aquastat controls are "crossed" incorrectly so it won't heat your home: the fix is easy

@Clare Martinez,

You are absolutely correct that the aqua stat is not set properly. The way that it's set the circulator will never turn on. The high must always be at least 20° higher than the low. Set your high to 180 or 200 and the low at least 20° below that point.

A reasonable starting place would be to set the high to 180 and the low to 155.

Now with the aquastat set correctly, set your thermostat well above room temperature to be sure that it's calling for heat.

The circulator should come on and you should feel the water and the pipes returning to the boiler get hot.

Let me know how that works and if you still don't have heat we will continue from that point.

...

Resideo / Honeywell L7224U1002/U Universal Electronic Oil Boiler Aquastat FAQs

Help with aquastat settings - or with bleeding air from heating system - Fix an Airbound 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 HoneyWell 125017AAA7942
New aquastat Resideo HWL7224U1002
Oil boiler Weil-McLain
Boil ersize 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 Jim Hickey -

Reply by InspectApedia Publisher - Resideo L7224U1002/U Universal Electronic Oil Boiler Aquastat Diagnosis

@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.

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

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?

by InspectApedia Publisher - air trapped in heating lines blocks or partly blocks hot water flow

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.

We explain how to diagnose and cure air-bound heating boiler systems

at AIR-BOUND HEATING SYSTEMS  so check that out and then

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

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

by InspectApedia Publisher

@Jim

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.

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.

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.

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.

by InspectApedia Publisher - air bound heating systems

@Jim H

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.

 

Heating circulating pump wont run in one zone - is this an aquastat problem?

Good afternoon, I have Burnham Series 2A with 2 zones circulating pumps, 1 zone for the main house and one zone for one of the bedroom.

The main heat work fine, the bedroom I replaced the circulating pump and the thermostat but the circulating pump wont run.

I tested the pump by connecting it to 120V and it worked fine.

Replaced the old Taco Circulating pump007_F4 with a new model F5

I think my aquastat settings must be wrong. On 2022-01-17 by Sam

Reply by Inspectapedia Com Moderator - No: aquastat settings will affect ALL of your heating zones

@Sam,

If you are absolutely certain that the circulator pump does not run when installed then also ran normally when connected by itself directly to power, there's either a wiring error or a bad control relay.

Watch out: These circulators are so quiet that they can be running without you realizing it.

So the problem could be in air bound heating system zone, OR the circulator isn't running because the HI LO and DIFF settings on your aquastat are incorrect. Start with HI =200, LO=175, DIFF=25.

BUT IF the problem were in the aquastat settings, then ALL of the heating zones would be affected, not just some of them

Please take a look at the article AQUASTAT HI LO DIFF SETTINGS as it is a more complete answer to your exact question.

House not heating up enough with HI set at 180

My HI is set to 180 and my house isn’t heating up to what the thermostat is set for, the heat stays below 60° if I set it to 200 it’s better but still has a hard time reaching what the thermostat is set for? On 2022-01-08 by Jeff f -

Reply by Inspectapedia Com Moderator

@Jeff f,

1. Check your Aquastat settings as advised in the article AQUASTAT HI LO DIFF SETTINGS particularly, if you set the LO too close to the HI then the circulator can stay locked out and you won't get heat; the LO must be at least 20 deg F below the HI.

2. If the Aquastat settings are correct and the circulator then runs on a call for heat, your system may be air-bound.

In that case see AIR-BOUND HEATING SYSTEMS - home

On Cast Iron Boiler Keep the LO setting to keep the boiler warm and avoid leaks

About LO setting on cast-iron boilers.

I read that LO setting is set to let cast-iron boiler heat up without running circulator, in order to prevent a lot of condensation and rust. So LO setting lets boiler heat up first and only then to turn on the circulator. On 2021-09-20 by Aydar -

Reply by inspectapedia.com.moderator - keeping some heat in cast iron boiler even when not heating the building can avoid condensation

@Aydar,

You are correct that for cast iron boilers keeping some heat in the boiler even in summer time when you're not heating the building can avoid condensation and also leaks associated with Cooling and move the can and some boilers cause leaks at the push nipples between sections.

Elsewhere we recommended keeping some heat in the boiler for those systems.

However that was never the technical or main purpose of the LO control, it's simply a side benefit for those particular heating boilers prone to leakage between sections.

Aquastat settings are causing scalding hot water

My aquastat has one dial with two pointers on it. Also, it is not accurate, but be that as it may, I would never never never want the high limit set to 180 degrees! It was recently set to 140 by a service man, and the hot water will severely scald you.

I believe that if you can keep the water at the kitchen sink faucet around 125 to 130 it is more than hot enough. On 2020-12-21 by Doug McGarrett

Reply by danjoefriedman (mod)

It sounds to me as if your aquastat is not correctly set. But for heating efficiency (lower heating and hot water cost) a good design is to keep the boiler hot but use an anti-scald device to avoid unsafe temperatures at the building's plumbing fixtures.

Be sure to review the different purposes of the high limit and low limit and differential settings as explained in this article so that you understand what each of them does.

Then see our anti-scald burn safety advice

at ANTI SCALD VALVES & TEMPERATURE CONTROL / MIXING VALVES 

Reader thinks Aquastat settings over 180 are wasteful

Setting a high limit at 180 or above is wasteful. I set my high limit at 160. The lower boiler temp is unnoticeable in the home heating. Actually my oil bill dropped 25%. Low limit is always 20 degrees less than high limit. The furnace does not come on all the time as before.

My circulators stay on longer to move heat to baseboard pipes. The heat is very even in the house now. No pinging pipes. A water circulator is low power and costs 90% less to run than the boiler. I am completely happy and promote this to everyone I meet On 2020-11-13 by Jim McMahon -

Reply - by (mod) - You are Wrong, but several variables determine how efficiently we burn heating oil and thus heating cost

Thank you for your comment, Jim.

I agree that there are a number of variables that determine how efficiently we burn heating oil and therefore what our heating cost is. The greatest Improvement in most buildings is from stopping air leaks.

Watch out: However there's no getting around science which tells us that the thermal conductivity of water and thinned copper baseboards is exponentially greater at higher temperatures.

That means we got a more efficient heat transfer out of the boiler system and into the occupied space when the Border Water is hotter. That doesn't speak to the heat loss rate for the building at all.

Aye, that I read recently really stuck with me. Science tells us truth whether we choose to believe it or not.

For a boiler only used for heat (not hot water) how should I set the DIFF?

If I set the Hi at 180 and the Lo at 160 what should I set the Diff. at. I only use the boiler for heat. What could be causing the boiler to short cycle every now and then? On 2020-03-25 by david

Reply by (mod) -

David

Probably the way your aquastat is wired it thinks you've got a tankless coil in use for domestic hot water, so it keeps the boiler hot even when there's no call for heat.

See AQUASTAT LO & DIFF DISABLED

for some suggestions

Benjamin Wood-Oil Combo boiler doesn't heat the house with just wood

I bought a house with a Benjamin wood and oil combo boiler and cannot seem to heat it very well with just wood, does anyone know what the settings are for the triple aquastat and for the single aquastat - On 2020-01-22 by Adam

Reply by (mod) - settings for the triple aquastat and for the single aquastat

I don't, Adam, but you can give the company a call

Benjamin Heating Products
166 Junction Road, PO Box 2079
Springhill, Nova Scotia, Canada B0M 1X0
Tel: 1-800-565-5495 · Fax: (902) 597-3797
furnaces@eastlink.ca

and perhaps the company can give you a manual;

or see these product specs

FS 140 COMBINATION OIL/WOOD HOT AIR FURNACE [PDF] retrieved 2020/11/22 original source: http://benjaminheating.com/files/8113/1550/1314/FS_140-Eng.pdf

Boiler temperature goes 20 degrees above our HIGH LIMIT

I just put a new temperature gauge on front of my boiler and for an Aquastat setting of 180 for high the gauge temp goes up to 220 .

I set the aquastat to 160 low and high temp reaches 200 . So it's about 40 degrees off . The aquastat is a Honeywell L8124C and probably about 15 to 20 years old . Can i run it like this with the lower setting as long as it doesn't change ?

Where the Aquastat gets it's reading is from a tankless coil area that I don't use because i figured it was burst or broken inside when i moved in. So i set my differential to 10 down from 15 since i have a broken coil that I'm not using and trying to save heating fuel and money here in Maine where it's a long winter usually .

Going to check the temp reading when boiler comes back on,set to 140 low to still give it 20 degree diff from the high even though the high temp is way off maybe due to hard water buildup or something on the sensor on the aquastat .What might be a better Aquastat if I ever change the one I have ? On 2019-12-17 by Tim Clark

Reply by (mod) - dangerous condition needs prompt repair

Tim:

Watch out: this is a dangerous condition. If the boiler temperature is actually over 200F then on a normal residential heating boiler the temperature and pressure relief valve should open and spill.

So if that is NOT happening either the temperature isn't really 220 (the gauge is inaccurate) OR the TPR valve is unsafe and risks a dangerous, even fatal boiler explosion.

I would turn the boiler OFF for safety.

For these reasons you want to satisfy yourself that you know what's going on - the solution is NOT in the Aquastat itself it first is in measuring boiler temperature and in inspecting, testing, and if necessary replacing the temperature-pressure-relief valve (TPR valve).

Once those critical life-safety issues are resolved we can worry about

- temperature/pressure gauge accuracy (search InspectApedia.com for these phrases to read details)

- proper aquastat settings (article on this page)

- proper aquastat installation including of its temperature sensor that is inserted into a well on the boiler (maybe you're missing temperature-conductive grease)

 

How do I stop heating domestic hot water at my boiler

Great site! I aImost understand many of your aquastat articles.

I maintain a property that has an oil fired boiler that supplies both heat, via old school radiators and domestic hot water.
The place is seldom occupied.

I know that I can reduce thermostat settings to minimize heating expense, but I also notice a lot of fuel is being used to heat domestic hot water unnecessarily.

How do I reduce or eliminate the heating of domestic water, unless I want it?
Thank you for your help. On 2019-11-24 by Ed -

Reply by (mod) - If the domestic hot water is being produced by an indirect water heater

Ed

If the domestic hot water is being produced by an indirect water heater that's being heated by your boiler then there will be a separate aquastat control mounted on that hot water tank.

If the hot water for your building is being produced by a tankless coil then the aquastat on your boiler controls that setting. However for a tankless coil case, if no one is drawing hot water, the only thing you need to do would be to set the low limit down to its lowest number.

Same rule of thumb apply with a steam boiler, with a high/low limit aquatast?

Does this same rule of thumb apply with a steam boiler, with a high/low limit aquatast, with a 5-30 degree differential?. when the heating cycles just reaches its end(the point where the water is the hottest) the temp out of the mixing valve is maxed at 140, for a short period of time. so for aquastat i’m thinking somewhere around 180 for high limit and 15 on the differential? On 2019-03-23 by Dwain Mcmillion -

Reply by (mod) -

In my opinion yes

For other readers, a steam boiler may also use a tankless coil that's of course below the steam boiler water line.

Since it's making steam you can figure that the boiler temperature must be reaching 212 degF (at sea level).

 

How does the aquastat work when there is no call for heat?

So I'm confused here. In this article on this other webpage on this site, https://inspectapedia.com/heat/Aquastats.php, it says that, when there's no call for heat, a furnace always will turn on at 10 degrees below the LO set point and turn off when the temp reaches the low point plus the differential MINUS 10 DEREES.

In other words, the differential is added to the temperature at which the furnace turns on (10 degrees below the LO set point), not to the LO set point, as it seems to suggest above.

So above it says: If the LO is 120 and the differential is 10, the furnace will shutoff at 130. But according to the other article, if I understand it correctly, if the LO is 20 and the differential is 10, the shutoff is 120. In other words, a 10 degree differential always shuts off a furnace at the LO set point and a max 25 differential always shuts off the furnace at the LO set point plus 15 degrees, not 25.

The second explanation seems to be supported by the website https://forum.heatinghelp.com/discussion/82927/aquastat-settings

But that third webpage raises another point of confusion. It says the circulator is allowed to run at 10 degrees below the LO set point (the furnace-on point). Both articles on this site suggest that the circulator is not allowed to turn on until the LO level plus differential is reached, (differential -10 for the other page).

Can anyone clarify? What is right? Or am I just reading all this incorrectly - I'm not that smart :O) Many thanks Anthony Giorgianni On 2019-01-12 by Anthony -

Reply by (mod) -

Thanks for asking Anthony, I'll review the two articles and the details to be sure we express these temperatures and limits clearly.

What can be confusing is failing to note that we're talking about the Differential OR DIFF control - on a call for heat, the DIFF control will lock out the circulator at low temperatures.

IF an aquastat is wired and set up to keep the boiler hot for making domestic hot water using a tankless coil, THEN the DIFF and LO become important as they keep heat in the boiler for that purpose, and also because the aquastat will prevent the heating zone circulator from running to deliver hot water to radiators or baseboards while you're in the shower consuming domestic hot water.

Clarifying further, the "130" degrees to which you refer is mentioned in our explanation of the DIFF control and what that does.

Quoting:

Our photo 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).

Raised aquastat but heat is no better

My boiler aquastat is raised to 160 Hi and 140 LO because part of my second floor is not getting heat but I have not seen any improvement.

While the front half of the house radiators are hot the back part especially the second floor there is no heat. What could be the problem with the hot water circulation?
Thank you for a response On 2018-10-18 by Randy -

Answer by (mod) - when some zones heat and others don't the problem is not the aquastat

If one of your zones is getting no heat at all then the problem is not the settings on the aquastat on the primary controller.

That's simply controls the temperature operating range of the boiler.

More likely you have a zone Valve or circulator pump that is not working, or you might have an air bound heating Zone. If you can confirm that the zone is calling for Heat and the circulator is running and search this website for

air bound heating system

to see the diagnosis and repair needed.

 

Why is there a wide difference between aquastat settings and boiler temperature gauge readings

Great site and info. I noticed that my aquastat and my boiler temp gauge are a good 20 degrees different.

My Aquastat's HI might be set to 180 but the boilder temp gauge reads 200 before it shuts off then pending no heat is being called, it might heatsoak all the way to 220. I turned the acquastat HI down to 160 and that seems to make the boiler shut off at 185 and max heat soak i've seen was 205 in this configuration. Do I need a new aquastat or does my compensation method work?

Also, is it worth re-greasing the probe well to ensure the aquastat is in good contact with the probe well wall? Any other suggestions?

Another quick question... My boiler has a tankless water heater coil to provide hot water. Recently I had a tech install a 50gal storage tank. The storage tank has no wires going into the the aquastat of the boiler - the storage tank has it's own aquastat that turns a zone circulator on/off. The zone circulator is connected to the in/out of the boiler hot water coil.

Do I still need to set my LOW and DIFF on my boiler aquastat (and if so, can you recommend a setting)? What does the storage tank aquastat do in this set-up and how should I set that in conjuction with the boiler LOW/DIFF settings?

Currently my hot water measures a max of 155 - 160 degrees coming out of a faucet on full blast hot. Looking for some advice on settings that could save me some $$ in oil yet have little impact on current performance (I.E currently 2 simultaneous 10min showers without issue and plenty of hot left over) 12/30/2014 Ryan

Reply: a 20 degree variance between temperature setting and actual boiler temperature means something's wrong

Ryan,

While aquastats and boiler pressure/temperasture gauges are not lab-grade highly-precise instruments, a 20 degree difference may say something is wrong - or might be normal. It depends.

Certainly the HI or upper limit setting, say set to 180F should result in a boiler gauge temperature reading close to 180F when the boiler SHUTS OFF at the end of a heat-on cycle.

But not always. For example if the burner is firing but the thermostat call for heat is satisfied (the thermostat then turns "OFF", at that point the boiler will stop firing even though it has not reached the cut-off temperature.

But your boiler gauge readings of 20-40 degF above the HI setting suggests something's wrong. It could be a faulty temperature sensor, poor contact between the temperature sensor in its well and the sides of the insertion well (use heat-conductive grease provided by the manufacturer) or a faulty control.

It's possible the trouble is your boiler's gauge - it might be sticking. Because typically if the boiler were truly reaching abnormally high temps, over 200F, the pressure/temperature relief valve should be spilling. I might try installing a new gauge first.

For details on how to set the HI LO DIFF optimally, in ARTICLE INDEX see the article titled AQUASTAT OPTIMAL LO/DIFF SETTING - and let me know if questions remain.

Ryan

Thanks DanJoe. At the moment, the aquastat is set to 150HIGH and 120 LOW which is resulting in consistent boiler temps of 180 - 185 HIGH (even when heat soak comes into factor) and 150 - 160 LOW.

I don't notice the boiler temp gauge sticking, it swings very fluidly but I'll read into what it takes to replace the boiler gauge. Since the aquastat is consistently reading LOWER temps then the boiler gauge, I'm guessing (hoping) based on your response the aquastat is not touching the inside of the probe well. I'll take a look and re-insert grease where needed.

On the other subject I posted about: Boiler coil connected to storage tank; Do you have any thoughts there?
" Another quick question... My boiler has a tankless water heater coil to provide hot water.

Recently I had a tech install a 50gal storage tank. The storage tank has no wires going into the the aquastat of the boiler - the storage tank has it's own aquastat that turns a zone circulator on/off. The zone circulator is connected to the in/out of the boiler hot water coil.

Do I still need to set my LOW and DIFF on my boiler aquastat (and if so, can you recommend a setting)?

What does the storage tank aquastat do in this set-up and how should I set that in conjuction with the boiler LOW/DIFF settings?

Currently my hot water measures a max of 155 - 160 degrees coming out of a faucet on full blast hot. Looking for some advice on settings that could save me some $$ in oil yet have little impact on current performance (I.E currently 2 simultaneous 10min showers without issue and plenty of hot left over) "

Reply:

Ryan if the gauge seems OK I suspect that the temp sensor on the aquastat is defective or it is not in good thermal contact in the sensor well. Some heating service techs deliberately skipped the manufacturers' instructions to use a thermal grease when installing the sensor, complaining that the grease gets stiff and makes later control replacement difficult.

But I believe that the manufacturer knows what's most important in successful installation of their product.

Further, the current thermal grease has been improved and doesn't create a stuck-sensor issue any longer.

Ryan if you are using an indirect fired water heater with its own heating zone and controls, you can abandon the tankless coil and disable the appropriate parts of the aquastat - see

AQUASTAT LO & DIFF DISABLED

OR there are other options for using both the indirect water heater AND the tankless coil. For your set-up I don't recommend this, but one can pipe the tankless coil after the outlet from the indirect water heater so that the coil only comes into play as a booster unit if the first heater has run out of hot water.

I wouldn't do it.

A decent indirect fired water heater is efficient, a good use of the boiler as heat source, and most likely the added support of the tankless coil is not needed.

...

...

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

Or see these

Recommended Articles

• AQUASTAT CONTROLS - home
  • AQUASTAT HI LO DIFF SETTINGS
  • AQUASTAT LO & DIFF DISABLED
  • AQUASTAT RESET BUTTON
  • AQUASTAT SELECTION GUIDE
  • AQUASTAT TROUBLESHOOTING 
• MANUALS for HEATING & A/C SYSTEM CONTROLS
• SINGLE FUNCTION LIMIT SWITCH
• WATER HEATER TEMPERATURE ADJUSTMENT CONTROLS

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INDEX to RELATED ARTICLES: ARTICLE INDEX to HEATING BOILERS

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