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.

On 2019-11-30 by (mod) - furnace won't shut down even with tt unhook at wall and furnace

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.

On 2019-11-30 by Bruce

Electric furnace won't shut down even with tt unhook at wall and furnace

On 2019-11-09 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

https://inspectapedia.com/electric/DMM_VOM_Safety.php DMMs VOMs SAFE USE OF

and

https://inspectapedia.com/electric/DMM_How_to_Use.php DMM DIGITAL MULTIMETER HOW TO USE

On 2019-11-09 by Anonymous

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?

On 2019-11-09 by Terry

My Heat Pump is no longer working so we are forced to use our furnace for heat. We installed a new pro select thermostat in our house however when we turn it on to Heat we use emergency heat and auto fan and it will not turn off even when it passes the set temperature. We have push the reset button still no difference.

On 2019-03-11 by (mod) -

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.

On 2019-03-08 by Eb

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

On 2019-01-28 by (mod) -

Re-posting from private email:

Anonymous asked:

Hello..please help

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.


REPLY:

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

On 2019-01-06 by (mod) -

Frank

Did you try the steps suggested in the article above?

On 2019-01-03 by FRANK ZODNIK

thermostat won't shut off boiler. Cut power and turned back on and furnace ignites.

On 2018-12-22 by Mike

I have a Colman heat and air it is old but never had a problem with it till now the fan want shut off

On 2018-10-23 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.

On 2018-10-23 by Ray

Why does my fan come on before burner

On 2018-10-23 by (mod) - Why does my fan come on before burner

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.

On 2018-10-23 by Ray

Why does my fan come on before burner

On 2018-05-20 by (mod) - my therorator wont shut off i

There has got to be a circuit breaker or fuse for your heating system which would allow you to turn it off if all else fails. Follow the wires.

On 2018-05-20 by Nadine

my therorator wont shut off its broken and the steam heater does nit want to shut off no brraker for it.

On 2018-05-12 by Anonymous

What brand and model thermostat?

Post a photo.

the knob doesn't turn to off position even when its depress

On 2018-04-13 by (mod) - shorted thermostat wires or a defective thermostat.

That sounds like shorted thermostat wires or a defective thermostat.

On 2018-04-13 by Anonymous

Replaced batteries but same thing happens

On 2018-04-13 by Connie

My thermostat keeps going to heat mode when it's hot inside its see at cool 74

On 2018-04-07 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)

On 2018-04-07 by joanne

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 2018-01-22 by (mod) -

Doug

My best advice to start is to step through the suggestions on the page above, perhaps focusing on a check for thermostat wires shorted together.

On 2018-01-22 by Doug

So I replaced the thermostat six months ago and everything has been working fine Then I came home an noticed the house was super hot the other day .

I checked the thermostat and it was set for 65 and the house was 76, and the furnace was still running with heat. All the wires in the thermostat are connected. What else should I be looking for and trying? thank you...

On 2018-01-16 by (mod) -

Anon

See the two FAN WON'T STOP ... diagnosis and repair articles given in the Continue Reading links just above.

On 2018-01-15 03:07:25.636952 by Anonymous

Fan keeps running won't stop and no heat

On 2018-01-04 02:35:49.305522 by (mod) -

if you are located where it is extremely cold it's possible that the heating system is behaving normally.

you might want to look through the list in the article above where we give the reasons that heating system doesn't turn off when it should.

and don't forget to look at the temperature setting at room temperature reading on the thermostat itself. If the room temperature is getting above the set temperature on the thermostat then I agree that the thermostat is not turning the heat off when it should

On 2018-01-04 by Rita Bardill

Our heat is running but after a while it shuts off Repairman will come tomorrow for the fourth time he put new parts in even New Thermostat it is a qualified company

On 2018-01-03 by (mod) -

I agree with your hypothesis.

Check your Zone Bells 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.

On 2018-01-03 by Bonnie

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 2017-11-12 by (mod) - heat not shutting off no matter how they set the thermostat setting

Stacey,

I would expect that someone has shorted the two thermostat wires together. It's also possible the thermostat was actually damaged.

On 2017-11-12 by Stacey

Did anyone answer Dave's question about heat not shutting off no matter how they set the thermostat setting

On 2017-11-03 by (mod) -

If you wired red to the r terminal and white wire to the W terminal and the heat won't turn off I suspect that they thermostat wires are shorted together

On 2017-11-03 by Ross

Bought a new honeywell rth6360 I've only got two wires my heat won't shut off

On 2017-10-16 by Dave

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 2017-10-06 by Eva

I have installed a new heat pump this summer. the cooling system is completely working well. when put heating option then both heat pump or furnace heating are never stop even I turn the thermostat off. the heat pump and blower only stop when the thermostat switch to cooling option. what is wrong with my heat pump?

On 2017-03-15 by (mod) -

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.

On 2017-03-15 16:30:52.769776 by Jennifer

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 2017-01-07 14:03:27.278363 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.

On 2017-01-06 04:37:52.825588 by Kim

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 2017-01-05 by (mod) - Why did my heating keep working after I turned it off at the control unit

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.

On 2017-01-05 by Paul Hill

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

On 2016-11-20 by (mod) - heater safety controls

Col

Heating equipment includes (or it should) several levels of safety controls, including a control that detects unsafe temperatures or overheating.

A gas wall heater will normally contain a fan limit control that will shut off the burner (even though the thermostat is calling for heat) if the control's sensor detects that the temperature AT THE HEATER is so high as to be unsafe - risking damage to the heater (that could in turn result in fatal carbon monoxide poisoning) or risking fire.

Other controls at a gas heater, at least newer ones, include a gas spill switch at the burner and at the flue vent exhaust draft hood that detect gas spillage (say from a blocked chimney) and that will also shut down the equipment.

Once the system has protected against fire, there's not another control (other than the wall thermostat) that turns it off in response to indoor temperature.

What was the indoor temperature when you returned home? It may have been horribly hot, wasting a huge amount of fuel, but unlikely that those temperatures damaged the building interior.

I would want to know the brand and model and serial number of the heater you've got. With that information you can find an installation and service manual that describes the heater's safety controls. If the system is so obsolete as to be unsafe I'd replace it.

On 2016-11-20 by Col D

My old gas wall heater stayed on and when I got home home the house was very hot. Yes, it was shorted wires to the thermostat.

What would happen if I were gone for the weekend or on vacation and heater stayed on for days or weeks?! (my space is pretty small and the heater pretty strong).

Could my home and possessions be destroyed by ever increasing heat?! Is there a safer system or process I can implement?

On 2016-11-19 by (mod) - shorted two wires together

Perhaps you have shorted two wires together, Dana.

On 2016-11-19 by Dana S

I installed a new Honeywell thermostat and now the heat will run but will not shut off when reaching the set temperature. I have to tire the switch from heat to off for it to shut off. All wires are tight

On 2016-11-10 by Michelle

I have the Internet 1100 series in my mobile home, I got the pilot lit and it will start the burner and the blower will work the problem is when it gets to the desired temp the blower shuts off but the burner won't it keeps going untill the blower turns back on it a vicious circle and the only way to shut it down is to turn off the furnace as a whole

On 2016-09-25 by Mary Jane

I have a Honeywell thermostat when I turned on the furnace thermostat was set to off but it heated the room to 70. What can I do.

On 2016-06-14 by (mod) - I have electric baseboards, heat has been turned off for weeks,

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

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.

Search InspectApedia for ELECTRIC BASEBOARD HEAT to read details.

On 2016-06-14 1 by Anonymous

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 2016-01-27 by Patti

The furnace is not satisfied when it reaches determined setting. It shuts off....a few seconds....then starts....rounds two minutes....turns off....repeat. So... If we set it at 70...it runs to hit that mark...but then doesn't seem to know to stop....it can't remain satisfied . We've replaced a one year Honeywell thermostat...and the problem exists.

On 2016-01-11 by ken tarzwell

Got a new honeywell 5 2 digital thermostat. Wont stop running the heat.
Old had y rh gr and white connected to b
As the inscructions. All were hooked the same
Gas/ac blower
No aux or em heat
Any ideas?

Live chat wanted me to chase unit wire in wall to see where it goes. Said inproper wiring

Not too sure

Bought rth2510

Kentarz@yahoo.com

On 2015-11-26 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.

On 2015-11-26 05:33:22.315507 by AJATX

Hello, 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 2015-11-23 14:21:49.882473 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.

On 2015-11-23 by Confused in SC

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 2015-11-21 by (mod) -

Sounds like a defective thermostat or one that is not properly located.

On 2015-11-21 by Ferroli Optimax HC 31c

Hello, when my radiators are switched on it keeps rising above its peak temperature going up to 60c when I put maximum temperature of 30c. I have been thinking about replacing the flow sensor or the return temperature sensor.

Thanks.

On 2015-11-19 by (mod) -

Anon you've posted this question in several pages - please save us work by asking in just one place; we have thousands of queries to which we need to respond.

If the heater blower is still running then power is not OFF to that device.

Check for a manual fan ON switch that is in the manual ON position.

On 2015-11-19 by Anonymous

Heater is turn off but still blowing cold air

On 2015-11-17 by (mod) -

Yep some fellows love the delivery-route idea. My mom, suffering from dementia, was paying Bob the crooked electrician (in Boca Raton) thousands of dollars to keep replacing lightbulbs.

Call your service company, speak politely and calmly with the service manager, and ask for a more experienced technician who can find and fix the trouble.

On 2015-11-16 by Anonymous

I keep having the service man come out for the same reason and 30 days later I have the same problem so what should I do because they keep charging over a hundred dollars.

On 2015-10-23 9 by Anonymous

I changed my them

On 2015-08-02 by (mod) - it's easy to confirm whether or not the thermostat is the problem when A/C won't turn on.

Mary

Usually it's easy to confirm whether or not the thermostat is the problem when A/C won't turn on. The thermostat is basically operating as an ON-OFF switch.

It can be opened or removed and the cooling wires that it would have switched can be jumped together - DONT TRY THIS if you're not trained as you might damage a control - rather let your servicve tech make the test; S/he may also do the same test by disconnecting the thermostat wires at the cooling appliance and making the same jumper test there.

On 2015-08-02 by Mary

I have a multi 4 zone from honeywell. Three of the 4 thermostats work fine but the one in the back room will kick on but not kick off for ac. It will not get below 78* All the other zones come on and off with no problems. Any ideas as to why this is happening? I am thinking a bad thermostat?

Question: 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.

Question: heat keeps running even if I turn off the thermostat

(June 7, 2014) Billy-Joe said:
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.

(Nov 22, 2014) Chuck said:
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?

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.

Question: blank display on thermostat

(June 16, 2014) ijay said:
my thermostat shows no display

Reply:

iJay

When a room thermostat display goes blank the usual reason is that electrical power is off to the heating or cooling system to which the thermostat is connected. Also check for a dead internal battery in the thermostat.

...

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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THERMOSTAT WON'T TURN OFF FAQs at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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INDEX to RELATED ARTICLES: ARTICLE INDEX to HVAC THERMOSTATS

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