Diagnose & fix heat that won't turn off when it should: here we discuss various causes of too much heat or of a heating system that does not shut off whenit should.

We explain how to diagnose and fix thermostat switch settings, switch settings right at the air conditioner or furnace air handler, and we review thermostat wiring problems that cause a heating system or cooling system to stay ON when it should not.

We provide a sequence of diagnostic steps that determine if the problem is at the thermostat, the thermostat wiring, or at other heating or cooling system controls.

Thermostat Troubleshooting: heating or cooling system won't turn OFF

These questions and answers about a thermostat that won't turn off or heat that is stuck ON were posted originally

at THERMOSTAT WON'T TURN OFF - be sure to review that article.

A separate article, HEAT WON'T TURN OFF, gives diagnostic procedures for other reasons why building heat wont' turn off besides problems at the thermostat itself.

Our electric baseboard heat is supposed to be OFF but I woke up to an electrical smell and the baseboard is VERY hot@

I have electric baseboards,heat has been turned off for weeks,I woke up to an electrical smell and the baseboard is very hot to touch and heat is coming from it? On 2016-06-14 by Anonymous

by (mod) - Safety warning

ANON:

Watch out: find the circuit breaker and TURN OFF your electric heat IMMEDIATELY to reduce the risk of a house fire.

Go to your circuit breaker and switch off the breakers that area marked as for electric heat - or if you can't figure out which those are, turn off the MAIN SWITCH in the electrical panel.

That will usually be the biggest switch at the panel top or bottom, or if you can't figure that out, just turn off every switch immediately.

Watch out: if you see fire or smell smoke get everyone out of the building and call your fire department.

This is no time to be reading stuff on the internet, but if no one knows how to do this more details are at

MAIN ELECTRICAL DISCONNECT 

You'll need a licensed electrician to find and fix the trouble; it may be as simple as replacing a control thermostat but you need to know that the wiring is correct, safe, not damaged.

More details are at ELECTRIC BASEBOARD HEAT

 

Furnace won't shut down even with tt unhooked at wall and furnace

Electric furnace won't shut down even with the thermostat unhooked at both the wall and at the furnace ! On 2019-11-30 by Bruce

Reply by (mod) -

Bruce

With the thermostat wires completely disconnected at your electric furnace we know that the problem is not the thermostat or its wires as that the problem therefore is in the relay or control that operates the furnace itself.

It's virtually certain that that relay or control will need replacement.

Meanwhile for safety you could turn the system off at the power switch in your electrical panel.

Followup by Bruce

Unfortunately that is exactly what we’ve been doing the last few days. We turn it on while home and turn it off when room reaches desired temp. Is it a bad thermostat?

Reply by (mod) -

Sorry Eb. It's rarely the thermostat but I guess possible.

Basicalliy the TT is nothing but an on-off switch responding to room temp.

If you disconnect the TT AT THE HEATER and the heater goes off the we know that most-likely that the problem is either the thermostat itself OR the thermostat wires are shorted enroute between the wall thermostat and the wire connection at the heater's control board.

Simple test for shorted thermostat wires:

I would test the TT wires for a short together.

Disconnect the thermosat from the wires at the wall and leave the two TT wire ends apart - not touching

Disconnect the thermosat wires at their other end, at the control board, and leave the two ends apart - not touching.

Then use a DMM or VOM in OHMS mode to see if there is continuity between the two wires - check both pairs of ends - if you see anything other than infinite resistance then the wires are shorted together somewhere enroute.

See

DMMs VOMs SAFE USE OF

and

DMM DIGITAL MULTIMETER HOW TO USE

 

We replaced the thermostat and now our living area is too hot - and the heater won't turn off

Our living area has been really hot and the old thermostat did not have an ON/OFF switch. We changed the thermostat today and switched it off but the heater is still on. We cannot find a reason why and we have verified the wiring and all is correct.

Is it possible that something else may not be working? Maybe the transformer or some kind of regulator?

Reply:

First disconnect the thermostat wires right at the heater itself, at it's control.

That's the same as turning down the thermostat. If the heater stops then you know the trouble is in the thermostat wiring thermostat settings, is the thermostat itself.

As your problem showed up after installing a new thermostat, I would be sure to check that you made the right connections, that the thermostat switches are properly set, AND that the thermostat wires were not accidentally shorted together.

IF that doesn't identify the problem see our complete guide

at HEAT WON'T TURN OFF

How do I force my heater to turn off while I wait for the repair person?

Good day my thermostat stopped working couple days ago.

The heat is still pumping. I turned it off 3 days ago and it still hot.

I have to keep opening the windows to keep it from reaching around 90 degrees please help I don’t know much but I do have 3 little ones and I just wanna keep them safe

by (mod) - use the furnace power switch(es)

Eb

In an emergency and while you wait for a service technician to find your control or wiring problem you can of course always turn off a heating system right at the power switch for the unit or in the electrical panel that supplies power to the unit.

If you don't know how to do that, see our illustrations and explanation of how to find and use the heat or A/C power on-off switch at

ELECTRICAL POWER SWITCH FOR HEAT

Mobile Home Coleman Presidential furnace won't turn off

My mobile home propane furnace has a problem. Started about 2 years ago. The burner

sometimes will not shut off ? One day...all day all night or 2 days sometimes 3 days.

Then suddenly the burner will not go out when the thermostat shows the off position. Last night

(cold night, lows 20's) system worked perfectly. This morning around 10am, as the day got

warmer the burner stayed on after thermostat went to off. I have changed the regulator on

propane tank...new thermocouple...and thermostat. All seem to help but problem comes up

after a day or two. Have contacted local service people...but ALL HAVE REFUSED to come to

my place to help me. Claiming system is to OLD. System is a Coleman Presidential II model #

7663A series 859. Any help will be greatly appreciated. On 2019-01-28 by anonymous

Reply:

Before calling for service again, review these two articles:

THERMOSTAT WON'T TURN OFF - be sure to review that article.

HEAT WON'T TURN OFF - other reason s the heat stays on

Then call a different heating service company and assure them that you're willing to pay for the service call.

If money is tight, contact your local social services department for help.

In addition to checking for shorted thermostat wires your tech might check the gas valve at the heater

Why does my furnace blower fan come on before the burner?

Why does my fan come on before burner ? On 2018-10-23 by Ray

by (mod) -

Ray

If the furnace blower fan - that circulates heated air to the building - turns on before the burner then a control or relay is not functioning properly.

However some furnaces may use induced draft in the vent or chimney to establish draft before the burner comes on - (NOT a blower moving heated air circulating into the building's occupied space)

So first let's identify just which "fan" is coming on.

Why does heat stay on all the time in our top floor heating zone?

We have four levels in our house, each level has a thermostat.

For some reason the heat on the top level stays at about 25 degrees. We tried turning the thermostat down until we turned it right off. There's still lots of heat and I can hear water going through the radiators.

Thinking the thermostat must be broken, we took it off and there's still heat coming. Please let me know what you think is going on. Could one of the other thermostats be controlling the wrong floor. On 2018-04-07 by joanne

Reply by (mod) -

Most likely, Joanne, the cause of the inability to turn off heat in the problem zone is one of those listed in the article above.

I'd start by looking for

- a stuck zone valve

- thermostat wires that are shorted together (try disconnecting the thermostat wires at the heater or zone valve or circulator pump end rather than at the thermostat)

And review more help given at HEAT WON'T TURN OFF

One of our hot water heating zones stays hot even though the thermosta isn't callinbg for heat.

My forced hot water radiators are staying hot only in one zone of a 4 zone heating system even when the thermostat is not calling for heat so I think it might be the check valve for that zone staying open

For troubleshooting purposes if it was the circulating pump would'nt it cause all the zones radiators to be hot? On 2018-01-03 by Bonnie

by (mod) - explanation - if the zone is open even with circulator off hot water circulates

I agree with your hypothesis.

Check your zone valves visually if you can. Some models have a lever that will show the position of the valve and some can be manually locked open or closed.

Or the valve motor or valve body itself could have failed in the "stuck open" position. In that case, even with the circulator pump OFF, hot water may circulate through the zone by "gravity" or natural convection.

Details are at ZONE VALVES, HEATING - home

Heat won't shut off after I worked on the Thermostat

I was called in to see what was wrong with a families thermostat. It is the old type that you just turn the knob to the desired setting. The location of the thermostat is on the staircases wall where it gets bumped into alot as they go up & down the stairs.

I removed 2 screws & pulled out the thermostat leaving all wiring intact as it originally was.

I noticed that one of the screw wholes in the gang box has been broken out thus not allowing the screw to have a tight fit. I gently put in a larger screw to hold it in place while I ordered a g clip to fix the issue.

I got a call saying that the heat is not shutting off no matter how they set the thermostat setting & have gone to the extreme of shutting off power to the thermostat by turning off the breaker.

Can anyone advise me on this as I have not had time to get back over to the home to troubleshoot the issue. Your help is appreciated. My email address is dl.soc1969@gmail.com On 2017-10-16 by Dave

by (mod) - Check for shorted thermostat wires

Dave: start by pulling off the thermostat wires right at the heater.

If heat goes OFF then we figure that the thermostat wires are shorted either at the thermostat or somewhere enroute.

With the thermostat wire ends disconnected from one another and from anything else, your VOM should see NO continuity between them (infinite resistance).

After a new thermostat was installed the furance blower never stops

A man came in to fix our heating system. He put in a thermostat with no on and off switch. The blower is on 24/7 and we want to turn it off. How can we turn it off. It blows cold air when the heat is off and it's the winter time. On 2017-03-15 by Jennifer

by (mod) - here's what to check

Jennifer

I'm surprised if a thermostat has no way to turn heat or cooling OFF -
But
If you set the thermostat in heat mode to a temperature below room temperature and

- if the heater itself turns off (the burner) but the fan continues, then there's a wiring or control error,

or an additional FAN ON switch at the limit control in the heater is in the ON position (not all limit switches have that fan on feature)

- if the heater keeps running and the fan keeps running too and the thermostat is set well below room temp then I suspect the thermostat wires are shorted together or there's a control failure.

Heating Radiators get hot even with the thermostat turned OFF

we have an oil burning boiler system. Normally I have the temperature set @ 70 during the day and 68 at night. We have 2 levels in our home.

The downstairs radiators continue to pump hot air despite the temperature having reach its desired setting. So, I turned the thermostat off, but the boiler continues to kick on and produce heat. My downstairs is currently reading 77 degrees.. Please help. On 2017-01-06 by Kim

Reply by (mod) -

Kim

If you mean radiators, those are water filled - they won't be pumping hot air, so I'm a little confused.
If your air is forced warm air heat, then warm air is coming out of supply registers - louvered grilles in ceilings, walls, or floors.

If your heat is by radiators that stay hot even when the thermostat is not calling for heat then there is a problem with a boiler / heater control such as
a circulating pump that's not shutting off or a check valve that should be closed but is not. Ask your heating service company to take a look and keep us posted.

Why did my heating keep working after I turned it off at the control unit

Why did my heating keep working after I turned it off at the control unit On 2017-01-05 by Paul Hill

Reply by (mod) -

I'm not sure what you mean by the control unit. However you can eliminate the thermostat from the question by simply disconnecting the thermostat wires at your heater.

Watch out: I have also seen oil-fired heaters that continues to run even when electricity was turned off when there was also a leaky control valve in the fuel unit.

With an oil tank that is higher than the oil burner, it's possible for oil to continue to feed to the burner and low pressure by gravity.

Result was a week But continuing Flame.

Goodman furance won't turn off now that I replaced an igniter

Today I replaced the hot surface ignitor in the Goodman furance and now it wont stop after reaching the set temperature. I tried setting the thermostat to off position but the furnance kept going and same thing happened when i disconnected the red wire from thermostat.

Does it mean that the furnace control board need to be replaced due to relay issue or is thermostat causing this issue? Appreciate the feedback. Thanks On 2015-11-26 by AJATX

by (mod) -

AJ

Replacing an igniter - that is the device itself - ought not explain why a heater won't turn off. I suspect shorted thermostat wires or a damaged control.

Heat won't turn off after hubbie turned the thermostat way UP

We are living somewhere, where the heat and ac could be run in the same week ( we do not of course to save on costs but still). The past few nights (and early mornings) we have needed heat. I keep it lower but the hubs turns it up above 75F.

And every time he does this the thermostat seems to take on a mind of its own and we have to shut it off directly at the circuit breaker. Why is it as long as it stays at 74F or below that it does a fine job but one degree more and it shoots upwards of 85F if not caught in time? PLEASE HELP!! On 2015-11-23 by Confused in SC

Reply by (mod) -

I'm confused too SC.

However if you are running a heat pump system, compressors don't like to be cycled on and off rapidly, as re-starting against head pressure in the compressor unit can cause it to fail to start.

Check:

1. that you are not frequently turning the heat pump on or off - wait at least 30 minutes between such cycles

2. that the base heater on your heat pump is working = a job for your service tech

3. that the thermostat settings are consistent, i.e. set to HEAT mode.

Heat keeps running even if I turn off the thermostat

My old style t86a thermostat wont shut off normally. the only way to shut it off is to crank the heat to the max. I switched the wires around and still the same problem its a T 86a Honeywell thermostat. (June 7, 2014) Billy-Joe

Heat continues to run even after turning down thermostat.Temperature reached 80 degrees and then I turned off breaker that shut unit down. Should I replace the thermostat? (Nov 22, 2014

Reply:

Billy

I'd look for thermostat wires that have become shorted together. Disconnect and remove the thermostat from the wall.

Then if heat still runs disconnect the thermostat wires at the heater-end.

If heat still runs then the problem is in a control board or relay at the heater.

Chuck

Before replacing the thermostat check for thermostat wires that are shorted together.

 

Why won't our thermostat set heat back at night?

My thermostat heat WONT TURN OFF at night. It runs fine during the daylight hours. We go to bed with the thermostat set at 64. Once the house cools to 64 and the heat turns on ...

It wont turn off. We wake up and the thermometer reads 74 but the thermostat reads a lower inside temp.

So we turn the thermostat down to 60. It turns off for a few minutes and then back on and stays running..

A heating guy came out to look at it and says he cant find anything wrong. He has come out twice during daytime hours when it does work fine. Any ideas on why it wont shut off at night? On 2018-01-05 by jody

Reply by (mod) -

Look first for an incorrectly-set night time program - the night-time set back function is most likely found only in the thermostat itself.

 

Temperature sensor does not respond to the actual space temperature

I have a Honeywell round thermostat and the space temperature sensor does not respond to the actual space temperature. in order to turn the heat on or off one must adjust the set-point above or below 65 deg. Are there any tricks to breathing some life back into the sensor or is it time to replace the assembly? - Thanks, (Jan 4, 2013) Nick

I have base board heaters. 2 in my living room, one in each room and its two room apartment. The heaters are heating up on their own even when I am not turning on the thermostat. I am now receiving $200 monthly bills from the electricity company and a shut off notice because its so high.

I dont understand why they are doing this. Can someone provide some clarification on this situation as I do not want to be without power with my wife and kid. Thanks. (Jan 16, 2013) Larry Morris

My thermostat is working for AC. But for my heating system, it didn't turn off the heat at desired temp. What might be the problem? Any help? (Feb 18, 2013) Jay said:

I have baseboard-radiator heat, 3 different zone circulator pump so only the upstair is having the problem. I used GRUNDFOS UPS15-58FRCV 59896343 pump. After reading all these, looks like "check valve" is the problem, but is that my check valve in built with my pump?

If yes, the can I just fix the problem by replacing the circulator pump... Any help is appreciated. (Jan 24, 2014) Chike

My heater won't turn off despite trying all the advice given. What do i do? the heat is becoming unbearable.

Reply:

If heat continues when a thermostat is set to a temperature below room temperature, or when the thermostat is disconnected entirely then I suspect one of the problems discussed

at HEAT WON'T TURN OFF and

also HEAT STUCK ON BY CONVECTION

 

...

Continue reading at THERMOSTAT WON'T TURN OFF or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• CONTINUOUS BLOWER FAN OPERATION
• FAN ON AUTO MAN Thermostat Switch
• FAN WONT STOP - LIMIT SWITCH
• FAN WONT STOP - THERMOSTAT SWITCH
• HEAT WON'T TURN OFF
• SHORTING THERMOSTAT WIRES to ID R W B

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