House heats up but thermostat is turned off AND thermostat's battery is dead
How to explain this? Hours earlier I had adjusted the Hi and Lo settings in the resideo Triple Aquastat Relay. Coincidence?
Comments
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I would suspect your adjustments to the aquastat
NJ Steam Homeowner.
Free NJ and remote steam advice: https://heatinghelp.com/find-a-contractor/detail/new-jersey-steam-help/
See my sight glass boiler videos: https://bit.ly/3sZW1el0 -
@ethicalpaul Is there a way to reset aquastat? Turning the boiler off then on didn't stop it. Putting new batteries in the thermostat but keeping it turned off didn't stop it. Hi is set to180F, Lo is set to 160F.
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Do you have a tankless coil in the boiler for domestic hot water? I assume it is hot water and not steam(I could see a triple aquastat in a steam system with a tankless coil and a hot water loop added to the steam boiler).
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@mattmia2 and @ethicalpaul I'll try disconnecting the thermostat wire in the aquastat and re-connecting it. Customer service at resideo the aquastat company, formerly Honeywell, said some thermostats are designed to close the loop and call for heat when the battery dies as a safety to prevent freeze ups.
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Is the circulator running? The circulator will be running if there is a heat call from the t-stat or the relay is stuck. it won't be running if the flow check to keep it from heating on a dhw call is stuck open or was manually opened and you are getting gravity circulation.
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@mattmia2 The circulator was running. I removed the C1 connection to the blue wire from the circulator to make the circulator stop running. The house was four degrees hotter than the t-stat was set to call for, even though the t-stat was off and the battery was low if not dead. It's a LUX brand t-stat.
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What would cause the relay to stick? The relay is the aquastat I assume. How would one manually open the flow check?
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check for short circuits in the wires from the aquastat to the circulator.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0 -
sometimes the contacts in the relay will weld together from wear.
turn off the power, disconnect t-t or x-x or whatever the t-stat connections are called on your aquastat and see if that turns the circulator off, could be a short in the t-stat wiring somewhere, probably at the connection at the t-stat
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@HVACNUT, @mattmia2, @ethicalpaul, @Jamie Hall I'm not at the house now so I can't do anything. I'm waiting for my Taco 5000 valve body to arrive (hopefully today) and then I'm going back (hopefully tomorrow) to assess and correct. I will do what you suggest, put C1 back and disconnect TT.
Here's a conversation I just had with ChatGPT about this mystery. None of you will be surprised by it.Me to ChatGPT:
I went back to the house to adjust the Hi and Lo temperature settings. In doing so I momentarily turned the LO setting to 140F or below. When I did so, I heard a soft click. I then set the controls where I wanted, the standard 180F for Hi and 160F for Lo. I then leave the house with the boiler turned on. Hours later I get a text from the resident telling me the heat is on in the house. But that the thermostat has been turned off for a week and the battery is low if not dead. What happened?
ChatGPT said:Thanks, William — I’m with you. Based on your description, here’s what most likely happened:
🔧 What Likely Happened:
When you turned the LO limit down to 140°F or below, even momentarily, the circulator control logic in the Resideo L8124C1003 may have activated.
This aquastat has a feature where:
- If the LO setting is set too low or the LO limit is momentarily crossed, the system can engage the circulator independently of the room thermostat, especially when the tankless coil is in use or believed to be.
- It may interpret this as needing to maintain domestic hot water temperature and begin cycling heat.
Meanwhile:
- If the thermostat is off or has dead batteries, it won't be able to call for heat, but the aquastat can still independently drive the burner and circulator under its low limit maintenance logic.
🧠 The Soft Click:
That soft click you heard was likely the internal relay or bimetallic switch reacting to the low temperature setting you dialed, triggering the burner or circulator.
🔁 What Happens After:
Even though you returned the settings to 160°F/180°F, that brief dip below 140°F may have:
- Triggered a heating cycle under the aquastat’s low-limit logic.
- Caused the system to begin heating (especially if the boiler temperature had dropped slightly below the set LO during your adjustment).
And because the aquastat doesn’t rely on the thermostat for this part of its logic, the heat turned on anyway, even with the thermostat turned off or failing.
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@Mhow can I manually open and close this flow check you're referring to. Is the flow check the grey metal square in the middle, top of the aquastat that clicks open and you can see it move, when the boiler gets a heat call. Is that the flow check, I thought that was the relay?
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@mattmia2 What part of the aquastat is the flow check that keeps the circulator from heating on a dhw call? How do I unstick it or open and close the flow check? And could this (circulators running to heat the house, when only DHW calls) have started because I raised the dial setting on LO higher than the dial setting on HI for an instant. And if so, how can I un-confuse it?
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Did you put C1 back and remove the thermostat wires from TT?
If you have the L8148C, the Lo is to maintain temperature for the coil. It alone won't cause the heat to come on.
If you disconnect the wires from TT and the circulator shuts off, the problem is between TT and the thermostat. If the circulator stays on, it's a bad relay in the aquastat.
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the flow check is a device in the pipe or circulator that keeps water from circulating by gravity when the circulator is off.
since the circulator is on, this is not your problem.
your problem is that the circulator is on. this is either because the thermostat wiring or the thermostat itself is shorted or the triple aquastat is defective.
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This information is incorrect
🔧 What Likely Happened:
When you turned the
LO limit down to 140°F or below, even momentarily, thecirculator control logicin theResideo L8124C1003may have activated.This aquastat has a feature where:
If the
LO setting is set too lowor theLO limit is momentarily crossed, the system can engage thecirculatorindependently of the room thermostat, especially when the tankless coil is in use or believed to be.It may interpret this as needing to maintain domestic hot water temperature and begin cycling heat.
Meanwhile:
If the
thermostat is off or has dead batteries, it won't be able to call for heat, but theaquastat can still independently drive the burner and circulatorunder itslow limit maintenance logic.🧠 The Soft Click:
That soft click you heard was likely the
internal relay or bimetallic switchreacting to the low temperature setting you dialed, triggering theburner or circulator.🔁 What Happens After:
Even though you returned the settings to 160°F/180°F, that brief dip below 140°F may have:
Triggered a
heating cycleunder the aquastat’s low-limit logic.Caused the system to begin heating (especially if the boiler temperature had dropped slightly below the set LO during your adjustment).
And because the aquastat doesn’t rely on the thermostat for this part of its logic,
the heat turned on anyway, even with the thermostat turned off or failing.This answer may be from an AI bot and has no basis in fact. The L8124 control can not do what that answer says it can do. The only way the
circulator can operate is if the 1K2 contacts on the K1 relay inside the L8124 is connected (operating properly) or welded together (defective). Adjusting the low limit will have no way to power the circulator. The low limit only has the ability to stop the circulator from operating. That happens when the water temperature is below the low limit setting and R to W is open and R to B is closed to operate the burner to raise the water temperature.
The 1K relay in the L8124 relay can only be activated by the thermostat circuit (T to Tv) or (T to T) circuit being completed. 1K2 contact can only be closed when the 1K relay coil is powered. See the Blue dashed line from L1 power to C1. the circulator can not operate with 1K2 contacts open
Nowhere in your comments here, do you mention that you have a L8124 aquastat relay. You must have mentioned it to the ChatGPT. So to be clear, what is the actual part number of your aquastat relay? If the thermostat circuit circuit is not getting a call for heat from a thermostat or zone valve end switch, and you have power to C1 on the aquastat relay, then the relay is defective and should be replaced.
@HVACNUT has the proper test procedure above. Remove one of the wires from T T and connect C1. The circulator should not operate. If the control does not power the C1 when you disconnect T T wires then you will know that your problem is in the zone valve wiring. Somewhere in the zone valve wiring there is a completed connection between T and T. That would be my guess!
So to be clear, what is the actual part number of your aquastat relay?
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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@EdTheHeaterMan L8124C1003
I did that test. With one T-stat wire disconnected at T and blue circulator wire connected at C1.
Result: circulators are running, and baseboard pipes are hot in living room.The only way I could get the circulators to stop running was either to let the boiler temp get below LO temp setting or to disconnect C1.
I bought and installed the aquastat on Monday, April 14th. With the T-stat turned off, the circulators didn't start running to heat the house until Saturday April 26th. The only thing I changed just before they did was I adjusted the HI and LO temp settings. Maybe even mistakenly turned the LO setting higher than the HI setting for a moment with the power on.
And just now, two days after leaving the house with TT connected and C1 disconnected, the resident is texting me that the aquastat is making the something-is-wrong buzzing sound and she has turned the boiler off.
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You are either going to have to start intelligent troubleshooting — or hire someone who can.
It's not rocket science. Start at the circulator which is running when it shouldn't be. Trace it's power wires back to what ever controls it. At the control there will be a power feed — and a control feed from something else. Disconnect the control feed from something else. Circulator stops? Wonderful. Now trace back those control wires to whatever. Disconnect them at that end. Circulator stops? Wonderful. Circulator doesn't stop? Problem in the wires.
And so on.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England1 -
That Resideo L8124C1003 is defective. C1 can not have power unless T T is connected with a jumper wire, thermostat or the end switch of a zone valve or otherwise connected. although Electronic parts are often not returnable, you should try to take it back to the place you purchased it and say it was defective out of the box.
This is the lower cost better replacement for that control: L7224U. You will want to measure the voltage that is coming from the wires that you connect to T T before you connect them to the aquastat. There should be no voltage on those wires from the zone valves or thermostats. If those wires are sending 24 volts to the T T, that is a problem. Those wires should only be open or closed, never powered. That is because the power for this circuit comes from the L7224U (or from the L8124C) itself.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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@EdTheHeaterMan, @Jamie Hall The only wires from or to the circulator are a romex sheathed blue and a white wire. The blue is connected to C1 and the white to C2. There are no other wires.
See pic.
I bought the aquastat to replace the pre existing aquastat of the same model that had gotten wet when the Taco5000 mixing valve, mounted directly above it, dripped on it. The mixing valve began dripping as did the cold water coupling to the boiler coil, after winter. The resident bragged she only spent two hundred dollars on oil. And this is in New Hampshire.
The tech company I hired to approve my installation work, on April 14th, took the cardboard box the aquastat came in. I don't know if Home Depot will take it back without the box. The tech didn't ask, he just took it. The tech also snipped a forked tap wire coming from the boiler and landing on L1. He then nutted the stub of that wire together with the red wire coming in with L1 from the switch and down stream from the power vent, going out through burner romex not making any connections inside the aquastat. The tech said he was correcting a mis-wiring, a safety bypass, he called it, done by a previous tech simply because it was easier. All I know is that it had functioned perfectly for fifteen years. Two days later, when the device began to hummm that something-is-very-wrong electrical sound, I restored the L1 tap coming from the burner and for a week all was well, up until the morning of April 24th when the resident told me the house was heating up and the t-stat was turned off.
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Something is miswired — but from the descriptions I have no idea what.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England1 -
@EdTheHeaterMan The circulator was running with T disconnected and there are no other wires but the blue and white wires connected at C1 and C2 coming from or going into the circulator.
ChatGPT is too good to be true, I guess. I heard it hallucinates but why then make it sound so confident? Can't they train it to admit it doesn't know enough about a subject to be helpful?
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ChatGPT is the modern day version of a 'Confidence Man'. " Can't they train it to admit it doesn't know enough about a subject to be helpful " I understand it does if you correct it.
If the T-T is disconnected at the Aquastat and the Aquastat is wired up correctly the relay 1K (coil), 1K2 (contact) is the only thing that can turn on the circulator at C1 and C2. (assuming the aquastat is the only circulator control).
Is there a wire pressing on the relay's armature causing it to stick in the active position ?
Good pictures inside of the Aquastat please. You can post them here.
National - U.S. Gas Boiler 45+ Years Old
Steam 300 SQ. FT. - EDR 347
One Pipe System1 -
@109A_5 Pics inside the aquastat before I replaced it. This worked perfectly for fifteen years. This is how I restored it after undoing the changes the tech made after audible malfunction signal. So this is how it was and this is how it is now.
A wire resting on the relay? The tests have been conducted with the cover off, so I say, No. Could you help me identify which relay you are referring to? I am only aware of one metal mechanism that visibly moves, or snaps open when the boiler is energized.
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There is only one relay, the aluminum colored part of it has "Honeywell" recessed in it. The Relay has three parts to it, the control section, the coil (1K) and two independent contacts or switches, 1K1 and 1K2. The 1K2 section acts as the switch for the circulator.
With 120 Volts AC applied to L1 and L2 the transformer converts it to 24 Volts AC. The 24 Volts AC is used to energize the coil of the relay (1K). The coil of the relay is normally not energized. The Relay coil should only be energized when the T - T terminals are electrically connected. The T - T electrical connection is often applied by a thermostat or an 'End Switch' in a zone valve.
As a test, if no wires are connected to the the T - T terminals the coil of the relay should not be energized and the circulator should not run and the armature (black plastic and aluminum) of the relay should not move and the relay's armature should be in the same position as when the whole system is powered off.
The only time the relay's armature should move (the black plastic closest to the circuit board moves up) is when the T - T terminals are electrically connected (and the Aquastat is powered) or when the T - T connection is released.
Why is the Lo limit set so high ?
National - U.S. Gas Boiler 45+ Years Old
Steam 300 SQ. FT. - EDR 347
One Pipe System0 -
This does not look very healthy.
National - U.S. Gas Boiler 45+ Years Old
Steam 300 SQ. FT. - EDR 347
One Pipe System0 -
I can't really tell which pictures are the newer unit, most seem to have corrosion visible.
National - U.S. Gas Boiler 45+ Years Old
Steam 300 SQ. FT. - EDR 347
One Pipe System0 -
"I can't really tell which pictures are the newer unit, most seem to have corrosion visible."All pictures (above) are of the old unit. Notice at C1, lower left of screw head, a black dot on the circuit board? This is a burn mark. Water had gotten inside the box. This is why I bought a new aquastat to replace the one shown in the pictures above.
"Why is the Lo limit set so high?"
I have no idea why the LO limit was set so high. The oil delivery company was the last tech company to work on the system. Is it cynical to assume that higher LO limits means more frequent firings hence more oil consumed/sold?0 -
@WilliamJ , I would like to point out something about the technician that connected the wires to the control. If that was you then I am not criticizing your abilities and only wish to help you correct a bad habit. If it was the professional technician, I am pointing out that this particular tech is taking shortcuts and may also be lacking in their knowledge of how that control should be connected to the Primary control of the oil burner.
To get your new, replacement control to operate properly, here is the wiring diagram that you should follow:
The wires that are in the shaded sections from the Primary Control should be already wired properly. There are three wires from the oil burner primary that go to the L7224U (or L8124C). They are connected to L1, B1, and L2. To properly connect then you may use a wire nut to connect the L1 to the 2 wires that must be connected to L1, or with the L7224U there are square washers that will accept a strait in wire so you can put one wire on the left of the screw and one wire on the right of the screw. That is an acceptable wiring practice when the wire is between the square washer and the terminal surface.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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After looking closely at the photos that you posted I have a question about the 4 wires taht are in the inside the armored cable on the left side of the control.
I can tell where some of the wires go to and come from. There are 2 wires that puzzle me. I was hoping you can tell me where those other twi wires (labeled 3 and 4) come from and go to. It appears that they just pass thru the L8124C from one connector to another connector without any connection inside the L8124C.
Are you able to open up the covers at each end of those wires an photograph their connections?
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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@EdTheHeaterMan
"I was hoping you can tell me where those other two wires (labeled 3 and 4) come from and go to. It appears that they just pass thru the L8124C from one connector to another connector without any connection inside the L8124C."
3 is wire nutted to a short red wire with a slide on tab and connects at B1. 4 goes to a wire nut where it is joined with another red wire coming in with the burner romex cable. Neither red wire stops to connect with any terminal inside the box. 4 passes through the L8124C without making a connection. I presume 4 comes from the power venter relay.The 3 and 4 wires are both nutted. There are only two nuts in the box.
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" So this is how it was and this is how it is now. "
Well I was hoping for Actual pictures of " now " the Aquastat unit presently installed " and this is how it is now. ". Since you are presently having problems with the Aquastat unit that is presently installed.
Looking at the Aquastat unit that worked for 15 years until the system leaked on it does not help much with the present problem IMO.
National - U.S. Gas Boiler 45+ Years Old
Steam 300 SQ. FT. - EDR 347
One Pipe System1 -
When you say Power venter relay, art you talking ablut a motorized vent that exhausts out the side of the building? Most of those Burnham boilers are vented into a chimney that requires no additional means of exhaust. The natural draft of a chinmey will create the needed exhaust (suction) without a fan assist.
This particular additional accessory will make your system wiring diagram a little more complicated and can be confusing to a rookie technician that is unaware, and does not know to look for that accessory. That may be the reason the tech rewired the red wire and said it was unnecessary, when it actually is needed.
If you have one of those power vent accessories can you tell me the brand name (There are two different brands that are popular) and the model number of the relay box that operates the power vent fan.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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Without knowing the brand of the vent motor or the control kit, I took the libetrty of using the Field Controls CK-63 control kit for oil burner operation. If you have a different control, you can let me know and I will substitute the proper control kit for you.
This is important that the control kit is installed properly so that the burner motor does not operate unless the venter motor is also operating. If the burner motor can operate without the venter motor operating, then you can get soot to form inside the boiler, vent pipe, and the vent motor assembly. That will be a real mess to clean up so you don't want that to happen.
After you provide me with the correct control kit and venter motor assembly, you should print the diagram I provide you and place it near the burner for future reference. this will let other future technicians that you have a power vent that must be properly wired and not to bypass any of the safety devices built into the system.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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The issue is with an L8124C, but is that really what it is? I'm seeing the L7224. Why are we still doing this? You don't even need a meter for this one and it's not solved yet. It doesn't look good on my resume. Maybe we should start from the beginning.
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I'm kind of puzzled why a GOOD picture of the wiring of the ACTUAL Aquastat presently installed with the actual issue can can't be achieved. Avoiding where the problem is, is not going to repair anything.
National - U.S. Gas Boiler 45+ Years Old
Steam 300 SQ. FT. - EDR 347
One Pipe System0 -
@EdTheHeaterMan, @109A_5 Here are some pictures of the new aquastat after I restored the wiring to what it was before the tech snipped the black L1 tap coming from the burner and nutted the stub to the red wires that were passing through from the power vent to the burner. As of right now C1 is disconnected and T-T are connected.
These 4 pics are from April 18th.
Later I did some testing with ChatGPTs directions. For one of the tests I connected C1 and I disconnected one of the TT wires then jumped T T with an insulated needle nose pliers. The relay engaged immediately. I also did a couple of other tests. One for Voltage at B1and B2 both when TT is open and again for when it is closed (jumped); I got 120V when TT was jumped. Same results at C1 and C2. Those results were normal, if I'm following correctly. Yet the circulators are running to heat the house with TT open (one wire disconnected) which is not normal and not even explicable.
The 1K2 relay is new to me and since I can't see it as a physical object in the box, I have a hard time dealing with it in reality. Can it be stuck closed and that's why the circulators are running as if there's a call for heat from T-T? Should I tap it with a screw driver? It is the part of the relay nearest the circuit board, Ed said.
Ed, here's another quote from my long day testing the aquastat with ChatGPT. If I understand you correctly, you said, the circulators cannot run with T-T open (no call for heat from the thermostat). If I am understanding you correctly, here again, the AI bot is contradicting you:"Great question — and yes, manipulating the LO limit dial can absolutely affect the behavior of the circulator, since the L8124C1003 uses the LO setting to control circulator operation independent of the thermostat.
Here's how it works:
- When the boiler temp is above the LO setting, and T-T is open, the aquastat may still power the circulator to dump excess heat (called "low limit circulator logic").
- So if you're only using the boiler for domestic hot water (DHW), you typically do not want the circulator running at all when there's no call for heat from the T-T."
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This is how I left it on Thursday, May 1st. T-T connected, C1 disconnected.
I folded a small piece of red electrical tape over the end of the Circulator wire that would otherwise be connected at C1 and I folded a piece of yellow tape over the end of the neutral wire that came in with the t-stat.
Here is a picture of the T-stat which has been turned "off" since April 14th, so I was later told by the resident:I think the resident had the boiler shut down most of the winter to save money on heating oil. Last week she bragged to me, she only spent two hundred dollars on oil all winter. In any event, the boiler shows signs of having suffered thermal shock, i.e., the dhw coil coupling and the mixing valve leaks.
Last fall the boiler system was in perfect working order, never a drip, no corrosion. Now there's a puddle on the floor in front of the boiler. How am I going to fix this? Is it fixable?0
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