Photograph of a multi function combination control on a heating boilerAquastat Repair FAQs
Questions & answers about how to buy, replace, install, set-up, & wire heating system aquastat controls

  • AQUASTAT REPAIR FAQs - CONTENTS: aquastat repair questions & answers help operate, choose settings, & troubleshoot a typical heating boiler combination control aquastat like the Honeywell R8182D, the Honeywell L8124A, and the Honeywell L8151A.
  • POST a QUESTION or READ FAQs about Aquastats controls used on Heating Boilers

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Repair questions for aquastat controls on heating equipment, boilers or water heaters:

These heater aquastat questions & answers help you to understand how to set an aquastat's HI, LO, DIFF dials & how to troubleshoot & repair this heating boiler control.

This article series explains how aquastats work and what the different aquastat controls are, what they do, and how they are set. We define the HI LO and DIFF controls on heating boiler aquastats and explains what they do and how they work. We explain the location and use of the heating boiler reset button found on aquastats.

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Aquastat Diagnostic & Setting Questions & Answers

Aquastat hi limit controlRecent questions and answers posted in this FAQs page or at AQUASTAT TROUBLESHOOTING

On 2017-01-15 21:57:14.339189 by (mod)


I can't say from just your brief e-text if the problem is with the Honeywell C99 controller, a flame sensor, or another control or burner operating safety problem.

I think by "flame rod" you refer to an igniter system for gas fired heating equipment. IF that's the problem, for example if the igniter is sparking but not igniting the flame, I would replace it using a compatible replacement, perhaps the Honeywell Q3400A1024 30-Inch Igniter Flame Rod Assembly. (About $40. U.S.D.)

On 2017-01-15 21:39:53.698388 by Louis hood

I have a Honeywell c99-100 with flame rod keep shutting down boiler gets to about 160 have to reset

On 2016-12-11 03:51:20.664905 by (mod)

If you turn up the load limit and it still doesn't turn on your boiler then either the control is not working, or is Miss wired.

The control sensor is not glued in place in the center well, it is placed in a conductive grease. Only if your system is quite old might the probe grease be hardened and require some gentle manipulation to remove the probe. In that case you will need to replace the control.

On 2016-12-10 20:32:26.104318 by Hal

The oil burner w/R8182D Aquastat turns on with thermostat but not with low boiler temp. Is it aquastat or is it temp probe not making contact? System, Burnham/Beckett furnace, was installed 1987.If probe "glued" in place, how best to remove from hardend grease? Or is it the aquastat itself?

On 2016-10-31 23:52:14.370327 by (mod)


It's not technically difficult but there may be details you don't know and don't know you don't know. On the other hand, if you simply read the installation instructions that come with the replacement control you will be head and shoulders above, in ability, some people who install these controls.

Take care for electrical safety, and be sure to pay attention to the instructions about using a conducting grease and about properly positioning the temperature sensor in the sensor well in the boiler.

On 2016-10-31 23:33:43.570053 by Scott

Thank you........ I'm not a hvac guy, but consider myself handy. It looks like a easy hookup and also a upgrade from my r8182d. I'm going to give it a shot. Thanks again!!!

On 2016-10-31 20:53:04.860452 by (mod)


In the article links at the end of the article above see AQUASTAT L7224U UNIVERSAL

On 2016-10-31 20:52:39.835513 by (mod)

Scott: sometimes a power outage includes a voltage surge that damages electrical controls.

On 2016-10-30 15:59:40.609918 by larry

what aquastat will replace a honewell r8112d aquastat

On 2016-10-29 22:14:47.242356 by Scott

I recently had a power outage and my boiler won't come on for heat. I tried to push the reset button and nothing. I tested the lines going to the aquastat and power is going in but not coming out. It is a Honeywell r8182d......... Any help would be much appreciated.

On 2016-10-27 14:10:34.949081 by (mod)


I can only guess since you haven't said what type of heating system you've got installed nor given me the brand and model ofd the heating system controller. Here's an example that might help:

IF your system is using a Honeywell R7184 aquastat controller, and IF someone pressed the RESET button two times without a successful call for heat, THEN the indicator light will flash at one-second intervals, or as the control manual says at 1HZ 1/2 second off, 1/2 second on.

You can RESET the controller by pressing and holding the RESET BUTTON for at least 30 seconds. That should stop the green blinking.

Watch out: if still your heating system will not start and run normally, do not keep pressing the reset button as you could cause an unsafe condition. Instead, call your heating service company for repair assistance.

On 2016-10-27 13:45:48.455814 by DD.

My heater green light blinks. I tried to set but it back on blinking. What might be reason please?

On 2016-10-16 16:26:05.848655 by Lenny

My hot water became very hot even when I turn down the temp wheel on the aqua stat temp remained the same. I replaced the aqua stat with the same model new one Honeywell L4006A. The problem still exists. No matter where I set the temp on the 4006a the water stays hot 140 or above. I turned the temp adjust all the way down to the lowest temp and the 140 plus temp remains. I then checked the copper temp bulb to be sure it is all the way in the sensor tube and it is. Don't know what to do next.

On 2016-10-12 01:14:46.091711 by john

my boiler is 60 degrees at rest . if thermostat calls for heat , gas fires & circ starts . shouldn't the rest temp be higher ?

On 2016-09-30 00:00:59.040264 by (mod)


Some electrically-savvy techs used to replace a bad relay on an aquastat if that was the problem but few modern heating techs will undertake de-soldering and soldering of components on a circuit board; rather they swap the control out with a new or factory-rebuilt one.

For the case you describe: i'd double check the wiring connections. POWER OFF - there are electrocution hazards.

On 2016-09-29 14:14:42.052847 by Anonymous

can an acquastat control be repaired? My honeywell acquatat has quit running twice in the last six months. I can give it a very light tap on the side and it will start operating normally

On 2016-08-19 00:07:54.457730 by (mod)

Sounds like a wiring error; I'm not familiar with an oil burner that runs on 24VAC.

On 2016-08-19 00:00:13.464961 by Anonymous

24v to the burner / keeps fry n the Aqua Stat /we get .02 tithe burner and power fry Aqua Stat !!

On 2016-08-17 13:54:52.230898 by Anonymous

I'm confused Stu: are we discussing an oil burner? The motor runs on 120V not 24V. The lower voltage operates relays and controls.

On 2016-08-16 19:05:22.479535 by Stu McDonald

Can't get 24v to burner (output) have 120v in / Aqua stat relay part # is L8148E1265 any suggestions ??

On 2016-05-30 22:53:23.419117 by (mod)

Clyde nearly all repair techs simply replace the control.

On 2016-05-19 14:11:21.398054 by Clyde Edmonds

The repairman said he did not repair honeywell aquastats. I'd like to get my old one repaired in order to have an extra on hand just in case. Where would I find a repair facility? Thanksfor you expert advice.

On 2016-05-19 14:06:04.487112 by Clyde Edmonds

where can i get an aquastat repaired?

On 2016-03-06 22:26:04.607683 by (mod)


The page bottom CONTACT link provides an email for photos and further comment. Didn't you ask this question elsewhere, or have I gotten confused?

On 2016-03-06 22:25:25.619075 by (mod)


AUTHOR:Paul (no email)
COMMENT:I have a HydroTherm boiler with a Honeywell controller. I have 120 Vac on the transformer of the Honeywell controller but no output (24 Vac) to the zone valves. I can't figure out what's going on and I have no heat right now. Can anyone give me a clue what might be wrong? I can attach a photo but can't figure out how to do that either!

On 2016-03-06 17:01:05.871096 by (mod)


If you are referring to the reset button on an oil fired heating system most likely the problem is with the oil burner: an inadequate or faltering flae. DO NOT keep pressing the reset button as you could cause a dangerous puffback explosion. I'd call for service.

On 2016-03-06 17:00:15.625672 by (mod)


If the transformer is working and you see nothing at the zone valves I suspect an open or broken low voltage wire. Check and confirm voltage at the thermostats as well. You can email me photos using the page bottom or top CONTACT link.

On 2016-03-06 12:13:35.365922 by Kev

My overheat button knocks off boiler its a there a suggestion what might cause this

Question: "furnace" (actually boiler) kicks on but one circulator pump does not run

(Mar 30, 2015) rusty said:
I have a 2 zone heating system with 2 circulating pumps when the top floor is turned up the furnace kicks on and heats the top floor. when the first floor is turned on you hear a click noise from the t-stat and nothing happens went down stairs to boiler the circulation pump for the top floor is working and the pump for the first floor doesn't turn on. replaced the pump still not working.

Removed panel for the aquastat removed the 2 wires for t-stat. put a jumper wire on the 2 t-stat terminals. relay clicks but pump still doesn't turn on. bad aquastat?


If the circulator relay is not pulling in it's a bad relay or control.

If the relay pulls in and voltage is being delivered to the pump but the pump does not run it's most likely either an open wire or a bad pump.

(Mar 30, 2015) Anonymous said:
I wired the pump to a cord that plugs into the wall and the pump turns on.


So we know the pump is good.

Check the wiring for continuity and check all connections.

Check whether or not the circulator relay pulls in and when it does if voltage is given to the pump.

Watch out: there are electrocution hazards in what you already did and in what you might do

(Mar 30, 2015) Anonymous said:
all the connections look fine. when I used the jumper wire the relay moved in and when removed the wire the relay pulled back

Question: furnace (boiler) won't re-start after I change the temperature settings

(Apr 13, 2015) Anonymous said:
why does furnace fail to restart wehn i lower temp then turn back up



Is this a forced warm air furnace or a hot water heating boiler? The controls and behaviour are different.

In any event, if the thermostat is not calling for heat, that is if room temperature is above the thermostat temperature, then the boiler (hot water heat) or furnace (forced warm air) would not be expected to start.

Question: Burnam oil furnace (boiler) won't fire up regardless of thermostat setting

(Apr 22, 2015) Dennis said:
have a Burnham oil furnace that worked perfectly till mid April. now it will not fire up irregardless of which thermostat I turn up to try to get it to go on. The water circulation pump also runs constantly so I have the furnace turned off at the breaker box. Is it correct to assume that this is a problem with the aquastat and the repair is better left to a trained person. The furnace will be 24 years old this summer so would I be better of looking for a new furnace or just trying to get this fixed?

(Apr 22, 2015) Dennis said:
should be Burnham oil boiler, not furnace


Dennis, at AQUASTAT RESET BUTTON - we explain "How to Find and Use the Reset Button on the Aquastat Combination Control on a Boiler". Start there. That article also lists the location of all of the reset switches and buttons found on heating and water heater systems.

Question: furnace repairman said aquastat is not necessary - just wastes oil. Is that true?

(June 22, 2015) Anonymous said:
A furnace repairman suggested that having an aquastat on a furnace is a ploy by the fuel supplier that burns more oil than necessary. Is an aquastat necessary? His comment made sense, since hot water is not necessary all the time.



The aquastat is a critical control function on heating boilers and on some water heaters. It provides safety high limit temperature control as well as a low limit and differential control that assure heat in the boiler if a tankless coil is used on the heating system boiler.

See details about the HI, LO and DIFF optimal settings

However it is true that IF your heating boiler does not include a tankless coil, that is if you make domestic hot water (for washing and bathing) using a separate water heater, you may not need to use the LO and DIFF functions of an aquastat. In that case there are two options:

  1. You could replace the aquastat with a single function HIGH LIMIT controller, though the cost of doing on an existing heating so is in my opinion not at all justified given option 2
  2. You can simply disable the LO / DIFF feature on the aquastat. To do that - which costs nothing -

    Watch out: there are reasons to keep some heat in a heating boiler even when it is not being called-on to make heat or hot water, to prevent condensation, corrosion, solidification of deposits making them hard to clean, and because some models of older cast iron heating boilers may leak when left cold.

Question: Honeywell L8124C Aquastat adjustment trouble - water temperatures are abnormally high over 200°F

(July 28, 2015) Richard said:
I have adjusted the settings on my Honeywell L8124C Aquastat to a high of 160 a low of 120 with a diff of 20. yet the water temp soars to 190 and up to 205.....and it sounds like steam noise on inside of boiler. Tried closing return and draining with a hose to see if it was airbound....but after 100 gallons still a steady stream no bubbles. Could my aquastat be fried? Thank you.



Watch out: this sounds dangerous:

1. there is a risk of scalding burns to people using hot water

2. It sounds as if the limit control is not working properly or is not sensing temperature properly, Perhaps your service tech, like mine, does not like to use the thermally-conductive grease that assures good contact between the aquastat's temperature probe and the sides of the well into which it is inserted.

This is a ** DANGEROUS** situation.

Before giving up, search for AIRBOUND HEATING SYSTEMS and also for AIR DISCHARGE at FAUCETS to read about a couple of other conditions that might be occurring at the same time. But do not ignore that over-temperature warning.

Frankly I'd prefer to shut the system down pending repair.

(July 29, 2015) Richard said:
Dan I think and or am hoping for "airbound" the system was working fine until well pump failed and system had to be replaced. I am going to drain at bottom of boiler this time for air and take it from there. Thanks for the reply!

And considering the age of system.....Buderus might be the ultimate final step....;)


I'm not clear why air in the heating system would cause abnormally high water temperature levels. More likely air in the heating piping will prevent hot water circulation and you'd have cold radiators or baseboards.

Question: White Rogers Aquastat trips circuit breaker

(Oct 4, 2015) Ray Pierce said:
My white Rogers aqua stat reaches my set temp and trips breaker


Check for a short circuit on the oil burner, circulator, or zone valve circuits or a loose wire or a failing oil burner motor

Question: Honeywell R8182d aquastat ignores call for heat and boiler gets cold

(Oct 25, 2015) Anonymous said:
I have a Honeywell R8182d aquastat. On a random basis it seems to ignore a call for heat and consequently the boiler goes cold. Is this likely due to a bad control or could other things be causing the failure to fire? Like maybe dirty electrodes or plugged nozzle? Although why would this be an intermittent problem. Any ideas appreciated.


If the thermostat calls for heat on a hot water heating system the boiler may not run (in most U.S. installations) until the boiler temperature drops below the cut-in temperature controlled by the system's aquastat or primary controller.

But if the boiler never turns on at temperature drop, and doesn't even try to run then there is a control or wiring problem - provided it's not off on re-set. Check for an open wire in the thermostat circuit and check that the boiler will run if the therostat terminals are temporarily connected by jumper at the aquastat. Check also for a bad primary control or control relay.

Question: boiler temperature drops when the burner is fed cold oil

(Nov 15, 2015) Tajammul said:
My boiler temperature sudden drop when feed low temorature oil



Sounds like an oil burner adjustment or nozzle problem. Commercial systems use a pre-heater on the oil line but you shouldn't need that for residential heat.

If your "cold oil" refers to having just received an oil delivery, perhaps sludge stirred in the oil tank during delivery is clogging the oil filter or nozzle, causing the boiler to fail to run.

Your boiler needs service and/or repair by a trained service tech.

Question: Columbia boiler heats hot water but not the house

(Nov 21, 2015) Sean said:
My Columbia boiler (summer-winter hookup) will heat the hot water but does not seem to heat the house. The water temp hits 220 degrees and shuts off before hitting the set temp. on the thermostat. I just replaced the circulator and the problems still exists. Any ideas on what I'm missing here? Could it be the aquastat?

The aqua stat is a Honeywell L8124 L model and the Hi is set at 190, Lo is set at 160 and the Diff is set at 10.

Reply: aquastat behavior on a radiant slab heating system

Sean if the boiler heats up on response to a call for heat but the hot water is not circulating through the zones your system may be air-bound, or a circulator pump or zone valvce or circulator control may be inoperative. Search for AIR-BOUND HEATING SYSTEMS to see details.

(Nov 21, 2015) Sean said:
The boiler does not heat up on response to a call for heat from the thermostat. The only time the boiler will fire up is when the water temp nears the lo temp. setting. When I turn up the temp on the thermostat, it clicks at the thermostat and it clicks inside the aqua stat. The pump does not turn on and neither will the boiler. Brand new pump and I'm positive that it's installed correctly and wired correctly. I have floor radiant heat in a ranch house on a slab that is slightly over 1000 sq. ft.



Have you checked the circulator relay?

Radiant heated slabs use a mixing valve to avoid making the floor too hot for comfort. So if the floors get warm and hot water is circulating through the radiant system, the boiler will not always turn on immediately on a call for heat. But if the boiler never fires up and the floors and boiler are cold and your thermostats are calling for heat, I'd start at the AQUASTAT RESET BUTTON

(Nov 24, 2015) Sean said:
Anonymous-At the risk of sounding stupid, where would the circulator relay be located?

Reply: where is the circulator relay?

Sean no questions are stupid - what's stupid is to be afraid to ask. The circulator relay on a single-circulator system is usually in the primary control or aquastat. On a multi-circulator system there may be separate individual circulator relay switches, usually mounted near the circulator pump. Follow the circulator pump power wire backwards to find the relay or controller for the circulator.

(Nov 24, 2015) Sean said:
Anonymous-I found the circulator relays and there is no voltage. Good call. Sounds like the aqua stat needs to be replaced. Right now I have a Honeywell L8124L Triple Aquastat Relay. Looks like they don't make that model anymore. Any suggestions on a similar model?

Reply: replacements for Honeywell circulator relays or aquastats

Good going, Sean;

For replacing the Honeywell L8124L aquastat, the company points to the Honeywell L8124A/C and L8148A - or you can contact honeywell directly: See , contact your Honeywell distributor,
call 1-800-328-5111 or visit
Automation and Control Solutions
In the U.S.:
1985 Douglas Drive North
Golden Valley, MN 55422-3992
In Canada:
Honeywell Limited
35 Dynamic Drive
Toronto, Ontario M1V 4Z9

Question: circulator pump runs but boiler does not fire up

(Nov 21, 2015) tom said:
turn up thermostat circulating pump goes on but the boiler does not fire up checked water psi bleed everything



If circulator runs and boiler temperature drops but the burner never fires check the boiler reset control. See AQUASTAT RESET BUTTON

Question: using a Honeywell 1018 606C aquastat on a combined gas boiler and wood furnace

(Dec 7, 2015) dave said:
I have a Weil McLain gas boiler. The minimum setting for the aquastat is 140*. It is hooked up to a heat exchanger that is tied into an outdoor wood furnace. MY gas boiler would kick on when the circulators called for heat and the 3 zones were colder than 140*. I put a Honeywell 1018 606C aquastat on the water line coming in from the boiler and wired that directly with my aquastat on the gas boiler. I thought that would stop the gas boiler from coming on if the wood furnace aquastat was up to temp but it still comes on. Is there an aquastat I can put on the gas unit that would stop this? And why did my second auqastat set up do nothing?



I don't have a clear-enough picture of your wiring nor exactly where the second aquastat is installed to feel safe giving advice on this problem. I would like to see a schematic of what you've done, piping and wiring - you can send that by the page bottom CONTACT link if you like.

For a fast solution I suggest stopping by your local plumbing and heating supplier to ask their advice.

Watch out: ANY control wiring, mix, or application that is not what the manufacturer specified and designed is potentially dangerous. ON the combination wood/heat systems that I've inspected the manufacturer provided the controls they wanted us to use, specified their mounting instructions, gave wiring diagrams &c. A mistake could cause a fire or a fatal explosion.

Question: Boiler runs when I tap on the aquastat relay housing - or it used-to. What to test.

(Dec 20, 2015) Skip said:
Furnace does not turn on. Initially I would tap aquastat relay housing housing and furnace would come on. Then nothing. Manually opened switch in aquastst and furnace works fine, shutting off and turning on in cycles when hot limit is reached. Once I release switch the furnace shuts off. How can I test if switch in aquastat is faulty or if something like maybe cad cekll relay is not sending proper signal?



If the cad cell is not sensing flame it will shut the burner off about 15-25 seconds after the burner has begun to spin but no flame is confirmed.

If there is a good flame then the cad cell may be bad - usually the tech swaps in another one. Sometimes I try wiping soot off of the cell face. IF the face is sooty the burner is running dirty and needs service or repair.

(Dec 28, 2015) Skip said:
Thanks. Been lucky with warm weather here in northeast, turn unit on only for hot water. I prop open aquastat switch and it runs fine, flame and everything seems to work, cycles on and off as normal. However, I am certain "propping open" switch not a safe thing to do all winter. I close system down and shut off electricity for the night after heating up home. Will look for soot on cell face, but does not the fact that I get a strong flame and the system works fine with the aquastat switch propped open suggest either the aquastat or cad relay is the problem? Thanks in advance for your advice.


Watch out: Propping open an aquastat switch is dangerous. You are defeating a safety control: that can result in fire, explosion, injury or death.

If the flame looks good that's encouraging, though the smoke level could still be too high, or there could be a draft or unsafe chimney problem. In my opinion the system and its chimney, venting, combustion air, oil burner and control all need service, cleaning, and perhaps repair.

(Dec 29, 2015) Skip said:
Furnace serviced 11 months ago, I specifically asked to ensure chimney was working properly regarding air flow and draft, was told his test indicated all OK. He did mention potential problem with cad relay, for future consideration, but furnace worked all last winter with no problems, and we had a brutal winter last year. I am disabled and on a fixed income and cannot afford to have a service call costing hundreds of dollars hence looking to see if I can fix it myself.

Changing out aquastat or cad relay does not seem to require any complicated calibrations or anything, look more like disconnecting and reconnecting wires and properly inserting aquastat probe. I'm trying to narrow down which may have failed before spending the money on a new one. Estimate last year to replace cad relay was around $600, cost of unit seems to be a fraction of that, hence my effort to do it myself.

Would not try if I was not confident in my abilities, don't want to burn down my house. Checked chimney outside, no smoke issues, a sign I read might indicate other issues. If need be, will change aquastat and cad relay, but making an effort to see if I can narrow down problem before spending money.

Also, have carbon monoxide detectors and smoke detectors to alert if CO2 or smoke condition exist, fire extinguishers all over the place. These are day to day precautions, not a counter measure because of concerns over this situation. Not a total dummy, just sometimes.


From your notes it sounds as if a simple fix to try - very inepxensive, is to just swap in a new cad cell eye. It's a two-pin plug-in device in the burner tube.

(Dec 29, 2015) Skip said:
will try - Thanks! Happy New Year to you and yours!

Question: Replaced a White-Rodgers hot water relay with a Honeywell 8124 - no power at C1 C2 (circulator circuit)

(Jan 6, 2016) Wayne said:
Replaced a White-Rodgers hot water relay with a Honeywell 8124 because I had no power across C1 and C2 and suspected the relay was bad. I still have no power across C1 and C2. I have four H/W radiation zones, one circulator pump for the entire house. Can you advise?


Wow that's too bad. You replaced the entire control, so the problem is likely to be outside the control, in the power circuit to the control, to the circulator, or at the thermostat.

Try eliminating the thermostat from the equation by removing its wires and jumping the two TT connections right at the control. That should turn on the circulator. If it does the problem is in the thermostat or its wires.

Question: aquastat setting vs pipe vibration

(Jan 12, 2016) Anonymous said:
Can an improperly set aquastat cause pipes to vibrate


I doubt it. The aquastat turns on burner and circulator. Pipe vibration may be traced to a bad circulator pump or to poor pipe mounting or routing or even to water hammer.

Question: HydroTherm boiler with a Honeywell controller - no 24VAC at the zone valves

2016/03/06 Paul said:
I have a HydroTherm boiler with a Honeywell controller. I have 120 Vac on the transformer of the Honeywell controller but no output (24 Vac) to the zone valves. I can't figure out what's going on and I have no heat right now. Can anyone give me a clue what might be wrong? I can attach a photo but can't figure out how to do that either!



If the transformer is working and you see nothing at the zone valves I suspect an open or broken low voltage wire. Check and confirm voltage at the thermostats as well. You can email me photos using the page bottom or top CONTACT link.

Question / Comment:

(Jan 21, 2014) Hank said:

I have a Burnham V73 boiler with an L8124C control.The boiler has a gauge on the front that shows water pressure and temperature.I've read in the v73 manual online that the controller is supposed to be set at 210 hi and 190 lo but i have it set at 180 and 160 because at those temps it shows on the gauge on front it got up to 210 and sometimes tries to go higher and goes 20 to 25 psi.The relief valve was also blowing out steam when setting hi to 190 or above. Maybe i need a new aquastat control since the temp gauge and steam seem to be telling me it's getting too hot?

I forgot to say about the V73 that I am not using the tankless water heater since i think the coil inside has a leak that leaches water directly from the boiler into the water as far as I can tell.This boiler is in a home where the people left and all pipes froze and burst as i can remember water was still in the boiler also.Boiler could have some hairline crack inside or would water freezing inside it be enough to damage it or just the copper tankless coil?



On usual residential heating boilers, temperatures over 200 F risk spilling the releif valve. I'm surprised by that 210 F citation.

Question / Comment:

(Feb 13, 2014) Paula said:

Hi Just wondering if I'm about to get ripped off or should i tell this person not to do the work. I have a 1800 sq foot 2 story house and the farthest bedroom on first floor (2 outside walls) away from the furnace in the basement (consistently freezing cold outside) has been much colder than the rest of the house (tenants keep heat at 75 and this room hovers around 64-68) It's a gas furnace - He told me its a Peerless Boiler and he is factory authorized dealer and the date on the boiler is May 2012. I have hot water radiator heat. This new heating guy says the one year old Aquastat Control needs to be replaced - that it is a part failure unrelated to the workmanship of the previous contractor who did the work last year (i switched from Oil to Gas). That if he repalces the control that there is a 70% chance that this will solve the coldness problem in the back bedroom will get warm. If the whole rest of the house has been warm without any problem - is this really the problem, wouldn't the rest of the house be cold too? He wants to charge me $535 for the control 4 hours of labor at $65 an hour.

Now - its 2 days later, he did the work because my tenant was yelling and the property manager approved it. The room is still cold and now the contractor is saying the baseboard heaters were installed wrong and need to be 'reworked' for $450. He said that they are upside down and this is why the room isn't warm (same original contractor who put in the new furnace put in these baseboards in last year). I called the original contractor (wish i brought him over this time to begin with) but I'm working with a property manager now). He says that what this guy is saying is not true - that they were put in correctly. It was me who decided to use a 4' shorter length on one of the walls and this could be the issue, but why then did this new guy have to replace the control for $795? Do they Honeywell Aquastat Controls really cost $535 or is that way high? Thank you for any help or advice anyone can provide. -Paula


Paula we just replied to this question over at our Heating Baseboards page - please search InspectApedia for

Baseboard Heat

to see your question and our reply along with a photo of baseboard that is "right side up"

I can't understand how an aquastat would make one room on a floor cold but not the others, though indeed if a heating zone is quite long or piping runs through a cold area, the ending baseboards in that zone could be cooler than we'd like. But that problem would not be caused by the aquastat in a way that I can see. Details are in the article I cite.

Question / Comment:

(Feb 19, 2014) Jim Kyle said:

The circulator shuts off as soon and the burner shuts off. The installer says this is correct. It seem to me it should run for awhile to heat up the house. This is a new Aquastat.


Jim, what the circulator does may depend on how it was wired. And customs vary: e.g. in the U.S. vs Canada circulators are not hooked up the same.

If you are in the U.S. and your home heating system is wired as usual when the thermostat calls for heat that turn the circulator ON. The circulator will keep running until the thermostat is satisfied.

The temperature of the boiler water is what turns the boiler on and off. They are independent.

More: on many systems even if the thermostat stops calling for heat and thus stops the circulator, if the burner had turned on due to a drop in boiler temperature, the burner will typically keep on heating until the HI limit is reached

You don't say what controls are installed on your system, and I'm just nor sure what your installer did. You could take a look at the help telephone number for your boiler manufacturer or perhaps more directly, the brand and model of controls in use on your boiler to see if their specifications have been followed, or you could as the installer what the heck they did.

Question / Comment:

(Apr 13, 2014) bill freeman said:

the high cut off on my aquastat is set to 140. when the thermostat is calling for heat. the boiler goes up to 180 before cutting off. the longer it runs the higher the cut off will run. my diff is set at 10. can you help me please/ thank you


Bill it sounds as if maybe your Aquastat controls are crossed or not set properly. If the HI were set to 140 that ought to be the upper limit, right? Check the LO setting. Is it above the HI?

If not the control may be not connected properly or has a wiring error or is efective.

Question: Axeman Anderson M260 coal boiler troubleshooting

(Nov 6, 2014) Jennifer C. said:

Help! Have a furnace problem. I have an axeman Anderson M260 coal boiler. I can get it to work right. The only way I can get heat is if I plug it in. And the only thing that controls is the motor and the auger, and the shaker arm to shake out the ashes. Running it this way I control the heat. When the house gets to the desired temperature I unplug it. What I was wondering is if the Triple Aquastat relay would cause this problem. There is only one zone this controls. Any help would be greatly appreciated.

Reply: where to find help with an Axeman Anderson Coal Fired Boiler

I'm confused. How would the coal-fired boiler be expected to work if its coal feeding augur were not working - it'd have no fuel. Axeman's current coal fired boiler, the Anthratube, is described as fully automatic. Here is a copy of the boiler instructions

Perhaps you're saying that the aquastat should be controlling the coal feed and it's not? Tell me the model of the aquastat and perhaps we can comment on that control.

To contact Axeman for help:

Axeman-Anderson, Company
300 East Mountain Avenue
South Williamsport, PA 17702
ph. 570-326-9114
fx. 326-2152

Question: Burnham furnace with domestic hot water delayed ignition and booming sounds

(Dec 30, 2014) Mike Reilly said:
Have a Burnham furnace with domestic hot water. Was having delayed ignition when the furnace was starting but the service man replaced the transformer and that problem stopped. I am still getting an occassional boom out of the furnace inbetween heating cycles without a furnace start-up.Just a loud boom without the furnace starting or a demand for hot water or heat.Also, the Honeywell aquastat control always has a humming sound when the furnace isn't running. Any suggestions?


Mike a boom sound can presage a dangerous oil burner puffback. I'd ask for a service call. I suspect incomplete combustion or burner sloppy startup or shutdown. At the aquastat there may be a failing relay or transformer

Question: boiler short cycling causes

(Jan 13, 2015) Anonymous said:
What are the common problems to cause a hydronic boiler to short cycle (starts & stops)? Aquastat going bad?


Loose electrical connections, shorted thermostat, poor thermal sensor contact, as well as defective aquastat.

Boiler short cycling is discussed in the article above. Was that u clear or did you miss it?please take a look and let me know if questions remain.

Question: Weil McLain Boiler troubleshooting

(Jan 14, 2015) Anonymous said:
Hi I have a weil mclain boiler with 2 zone heating ( honeywell valves) . The zone valves work perfectly ( motors are working , microswitches good) . When i jump the thermostats , and the both valves energise, the bioler won't turn on. I was able to reset the boiler by turning it off , then would run for a couple of days but on he third day as the thermostats would be calling ( levers pressing on microswitches) for heat , the furnace would not turn on ( only turns on to manitain water temp per hi lo settings). Tried turning on/off boiler but would not work. Took cover off aquistat relay honeywell L8124A, and manually started boiler by pressing the Burner circulator relay plate ( something the thermostats should be doing) .. It started ...then afterwards the thermostats returned to normal firing up the relay on their own. ANy thoughts would be greatly appreciated / Thank YOu !



If on thermostat call for heat the zone valve opens but the heater does not turn on the end switch could be defective, but it'd be a surprise to have the same failure at the same time on 2 valves. A simple VOM or DMM test can indicate whether or not the end-switch on the zone valve is working or not. If it is, the problem is at the boiler or its controls.


(Jan 22, 2015) Paul Walter said:
Can not Identify my honeywell aquastat not number on cover horizontal


How would we do this from just an E-text; you're welcome to shoot us a photo and I'll see what we can identify.


Continue reading at AQUASTAT TROUBLESHOOTING that explains the best settings to use & how & when to disable the LOW & DIFF controls or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see MANUALS for HEATING SYSTEM CONTROLS for a list of aquastat installation & repair guides

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