Heating & Cooling Thermostat FAQs set 3, questions and answers on installing, using, or fixing heating or cooling thermostats.

This article series answers most questions about central heating system troubleshooting, inspection, diagnosis, and repairs.

Room Thermostat Diagnostic FAQs set #3

These questions and answers were posted originally

at THERMOSTAT DIAGNOSTIC GUIDE - be sure to see that article as it's the starting point for diagnosing and fixing problems with heating and cooling thermostats in buildings.

Our photo illustrates an antique room thermostat still in use at the FDR Estate in Hyde Park, NY.

On 2018-06-29 by (mod) - why does the thermostat have no power: display is blank

it's possible that your thermostat is taking power from the circuit that would be left open or off if a blower door safety switch is not securely made when you put the blower door back on. Check that first.

On 2018-06-29 by Anonymous

I was changing the filter on my trane air handler and when I put the blower door back on the thermostat was blank. The thermostat doesn't require batteriea and I made sure the circuit breaker is on. What else could it be? Thanks

On 2018-06-05 by (mod) - heat won't turn down no matter what

Monte, see

THERMOSTAT WON'T TURN OFF for the steps in troubleshooting and fixing the problem you describe

On 2018-06-05 by Monte

I live in a two-story apartments and there's baseboard heaters and I have a Honeywell thermostat but the heat will not turn off I tried turning down the thermostat but that did not work it's about 91° in this apartment how can I turn off the heat

On 2018-01-17 by (mod) - York heat pump won't give any heat

David,

I don't have enough information to make even a wild guess of why you have no heat, but there are diagnostic procedures that might help you at

AIR CONDITIONER (or heat pump) WON'T START https://inspectapedia.com/aircond/Air_Conditioner_Wont_Start.php

and

BACKUP HEAT for HEAT PUMPS - https://inspectapedia.com/aircond/Heat_Pump_Backup_Heat.php

and some very basic starting point things to check at

HEAT WON'T TURN ON https://inspectapedia.com/heat/No-Heat-Diagnosis.php

On 2018-01-17 by David Stevens

Have York Heat Pump...lately this winter I set thermostat to desire temp,it goes on but shuts off after a while thus never gets up to proper temp...sometimes doesn't even heat at all.

..tried switching to emergency heat but does same thing...the light on it to show the Temps goes out too what's up with all this....the outside AC part isn't freezing up and handler inside the house SEEMS to be the problem ?...appreciate any and all possible problems/troubleshooting on this..? ITS COLD down here !.....musicman014@g,ailco,

On 2018-01-04 by (mod) - fan keeps running

Vivien,

First check these two diagnostic articles for a FAN that WON'T STOP

and for FAN ON AUTO MAN Thermostat Switch

If niether of those is the problem, your system may have a bad fan relay or control board

On 2018-01-04 by Vivien

...and the batteries are new.

I had intermittent issues with my roof-top hvac...the system works great, but once reaching the preset temperature the gas goes out but the fan continued running.

I initially figured the thermostat itself might be the problem, so a year ago replaced that.

About 2 months ago the same thing started happening.

Not every time, but at least once a day I have to go to the mains fuse box and shut the system down to reset it, even if I internally switch it off the fan will not turn off, . Now I am not sure what to do.

Filters are kept clean, ducts are very clean, and the gas works as it should. I will add that only happens when the temperature is set between 67 and 70 degrees...

On 2018-01-03 by Anonymous

Thank you!

On 2017-12-30 by (mod) - thermostat switching between heating and cooling when it should not

Sounds like a wiring or control board problem

On 2017-12-28 by Jill

My thermostat is set to start heating the house at 5:00 AM to 72 degrees and set to shut down at 9:30 PM to heat to 67 degrees.

My unit is heating to 72 degrees and then it starts cooling to 67 degrees then turns around and starts heating to 72.

It cycles through this process without shutting off. My air conditioner is set to start cooling at 81 degrees and is set to the auto mode. If I turn it to the heat only mode, is this considered the emergency heat?

I have been told that if it's in the emergency mode my electric bill will go though the roof.

On 2017-12-15 06:22:50.562287 by (mod) -

This sounds like a defective thermostat. If replacing the battery makes no difference I'd try a different thermostat.

On 2017-12-15 04:37:03.897477 by Norma

We have a Honeywell digital thermometer. For some reason it is set to 90...and most of the buttons like hold schedule etc aren’t usable. I’ve reset it again and after a few minutes you can physically watch the temperature jump to 90

On 2017-12-07 by Kenneth

My thermostat started blinking and then just went blank and now the Heat and Air does not work

On 2017-11-18 by (mod) -

P

I'm not sure what's happening with your heating system and thermostat either.

However it is normal for the burner to not run continuously on an oil or or gas hot water heating system. That is, the burner will turn on in response to the temperature in the boiler not the setting of the thermostat.

In US homes thermostat turn on circulator to circulate hot water through your radiators or baseboards.

On 2017-11-18 by Pmr

My furnace works fine when the temperature set manually on the Neat TT but when I set temperature through my iPhone app, Neat shows the same temperature which my iPhone app
shows, but the gas chamber of the furnace does not stay burning

. The furnace starts, flame comes and shuts off in minutes. And when I shut off the furnace and start after 10 minutes manually it works fine. I am planning to reset the Neat TT.. hope that helps

On 2017-11-07 by (mod) - start by checking carefully all of the switch settings at the thermostat

Gary,

I would start by checking carefully all of the switch settings at the thermostat. It's possible that it has been set to cooling instead of heating mode.

On 2017-11-07 by Gary

Have a fuel oil furnace I put in new thermostat and had it serviced now last night my air conditioner is running constantly but the heater is working don't know what to do

On 2017-10-30 by Liz

My wall thermostat had many town settings and they are all set to 73 or 74 depending on the time. Every night for some reason my room temp will drop down in the 60s even tho I have it set to 73. Until I wake on the morning and reset it again. How can I make it so my heater stays on all night and maintains my 73/74

On 2017-10-29 by Susanne Li

I have just turned on my heat at the thermostat and set it to 21 degrees C. The HVAC until comes on. The unit blower is on.

The heat comes on but then after a bit, the blower no longer blows warm air and the temperature in the house will not raise over 19 degrees C. If I turn off the entire system, and then turn it back on, I get heat for a bit but then the same thing happens. The thermostat is at 21 but the house temp will not raise over 19. The heat just won't stay on.

On 2017-10-15 by Carol rist

Where do I get a response ?

On 2017-10-15 by Carol Rist

Why when I set my temperature does it say. Until 8:30 pm ?

On 2017-08-23 by Laura

We just purchased a new gas / air unit. It hasn't been staying at the temperature we set it on. It's either 2 or 3 degrees higher than what we set it on. Now today it's staying on the temperatures we have it set on . But now it not shutting off. It has been really hot outside in the 90s could this be what's causing this problem.

On 2017-08-06 by Michelle

The thermostat screen cool is on , but machine doesn't work .

On 2017-06-22 by (mod) -

Irene

A thermostat is basically and on off switch that turns heating or air conditioning on or off in response to room temperature.

If the thermostat is broken it may not be able to turn the heat or air conditioning on or off period however one could disconnect the thermostat wires at the heater or air conditioner and then connect the jumper wire between the two thermostat terminals at that heater or air conditioner to force it to run in an emergency.

On 2017-06-22 by Irene

If thermostat not working will heater still work

On 2017-06-16 by jana

hello-i have a rheem roof mounted unit in Phoenix. I will set the thermostat at a high temp at night in order to save on the electric bill; however

I am then awakened by cold air and a temperature as much as 10-12 degrees below the set temp. Programmable thermostat was replaced by my ac tech - problem did not go away. Replaced with a manual thermostat about a month ago, and problem continues to occur - seemingly randomly. Has happened four times in a month. Tech says this is impossible, but it's happening! any ideas? thx!

On 2017-06-16 by Lisa

My electric bill went from $98.00 to $394.00 in one month so I had someone come check out our central heat and air. On the display it says "control fault heater on" what would cause this and how can we fix it?

On 2017-06-14 by AmandaK

When I turn my account unit on in my house it doesn't blow cold. It's not hot but not cold an the switch is on cold but the aux heat red light will come on shortly after I turn the thermostat switch from off to cold?? Help please

On 2017-05-20 by (mod) - Try disconnecting the thermostat to rule it in or out of the problem

Try disconnecting the thermostat to rule it in or out of the problem

On 2017-05-20 by CHARLES

I have a carrier split 4ton unit with gas heat the honneywell digtal thermost is set on 75 but when it reaches 75 the unit still runs for 25 min before it shuts down what could be wrong

On 2017-05-09 by (mod) -

Shon,

If you mean that your heat pump provides heat but not cooling, that might be due to the outdoor temperature; for example if it's cold outside the and you call for cooling the heat pump might not run.

On 2017-05-09 by Shon

My thermostat is calling for the outdoor unit to come on when I switch it to heat but not when I switch it to cool but the furnace is responding according to the thermostat

On 2017-05-06 by Anonymous2

Are you heating by a heat pump? Is it quite cold outside? Your system may be trying to use its backup heat source and that's not working. Is call for repair.

On 2017-05-06 by Anonymous

My thermostat will not reach the room temp on the the thermostat desire . The house cool but the unit outsides continue to run because the desired temp I not being met . But if I cut the thermostat completely off the return area makes some diturving noises

On 2017-04-16 15:05:30.761189 by (mod) -

Marilyn

Be sure that the remote can "see" the wall-unit of your spit system and that it has fresh batteries. You should not need to recalibrate the remote, but if it doesn't have a clear line of sight to the wall unit it may not work properly.

Check the operating instructions for both the wall unit and the remote to be sure that switches on both are properly set. For example some wall units include a "test" or "manual" position that might tell the unit to ignore the remote.

If you don't have the manual for your unit use the InspectApedia search box just above to find our article giving links to HVAC MANUALS

On 2017-04-16 11:19:43.996539 by Marilyn

We have an LG mini split heat pump with a remote thermostat. The temperature settting is set for 20C in heat mode. When you press the room temp button, the temp displays at temp of 24 or 25C. Is there a problem with the remote? Why does the unit remain in heat mode for such long periods of time when the room temp reading is above the set point of 20C? Does the thermostat (remote) need to be reset or recalibrated?

On 2017-12-31 by (mod) - General Electric/Telechron Thermal Control

Retrodad,

Please use the picture frame icon to the right of the Comment button to attach some sharp photos of the exterior, interior, and wire connection points inside of your GE Telechron thermostat and I should be able to tell you just where to make connections.

Basically this thermostat is a clock-operated "on-off" switch that should be able to operate on a 24VAC circuit to switch the gas heater on or off according to the thermostat's settings for day and night operation.

On 2017-12-31 by Retrodad

We have a 1922 California Bungalow with a modern gas central heating system with one thermostat. During our ongoing remodel returning the bungalow home to it's former glory, we have utilized original appliances in the kitchen, etc. to the delight of all.

Recently, I purchased an antique General Electric/Telechron Thermal Control Manufactured in 1934 60 cyc. Model- M1 Type: B2 . It's in great condition and we would like to use it with our existing heating system. Is that possible? If so, how should we go about finding out the right way to have the unit replace the modern thermostat? Any suggestions, greatly appreciated!

On 2017-12-30 by (mod) - house won't get above 62

Anon:

You have my sympathy, I'm dealing with the exact same issue in our New York home at the moment.
Is your heating system forced hot water

- heating baseboards or radiators? If so you should follow the pipes and radiators from start to end to see if there is an area where piping gets cold - the system may be air-bound.

If you find that is the case, search InspectApedia for COLD RADIATORS OR BASEBOARDS to read the diagnosis and repair of the problem.

On 2017-12-30 by Anonymous

Hour will not get warmer than 62 degrees thermostat is set on 70 any help would be appreciated

On 2017-12-30 by Joe

My thermostat is set on 70, but the heat in the house won't get warmer than 62

On 2017-12-16 by (mod) -

Sbot

WIth the apology that the answer is only "ballpark" correct, you save about 3% on your energy cost for each degree F that you lower a room thermostat.

Dropping 2 degrees = 6%.

6% of 550 is about 33 gallons.

550-33 is 517 gallons.

Of course as the number of degree days varies year to year (probably falling as our global climate and local climates are warming), the actual savings you see will be a bit different.

On 2017-12-15 by Sbotcat

I use about 550 gallons of oil anually at 70 deg. App. how much would i use at 72 deg.?

On 2017-08-08 by Anonymous

How to check the thermostat level if there's nothing written , I mean it's the manual model

On 2017-08-05 by Nicky

I'm in need of some help! My thermostat downstairs is blank no power what so ever... when moving it to the upstairs to check it.. it works fine so it's not the thermostat. I've checked the breakers and they are fine although I did flip them off and back on... still nothing. I've read a lot of post and even watched videos on what to check and do.. I'm assuming the main unit is under the house but when crawling under there I see no switches or anything to flip.. however there is like a small breaker box when I opened it it has a red handle to something... I didn't mess with this because I sont kbow what it is exactly. I keep hearing about a fuse but I can't seem to find it... please help... it's so hot

On 2017-06-30 by Teena

Can you use a wall heater blower on a swamp cooler.

On 2017-06-15 by Stella

Hello, my mother has an older thermostat that is for the A/C as well as her heat. She and and I do not agree on the settings for the lever located at top of the thermostat. It has a lever for A/C and for heat. Then a second lever for ON and FAN. When setting the lever to A/C. my question is should the lever then be set to ON or to FAN?

My mother does not want to set the thermostat to auto. Instead she turns the air conditioner on when it is hot, then off when she gets cold. But she says the top lever should be switched to the FAN, I say it should be switched to ON. Can you please tell me what is the right way to turn an air conditioner on to cool the house?
Thank you in advance for any help.

On 2016-12-16 by Rob wb

I have an older honeywell unit I can't seem to get the pilot light to light and blower motor doesn't kick on. HELP PLEASE

On 2016-09-10 by john

what should allowable temp variance be when thermostat is set @74 degrees for 2000sf condo

On 2016-07-24 by Anonymous

cos on and off to fast

On 2016-04-04 by (mod) -

Good question, Anon. I have been unable to find

- a Caslant thermostat manual
- a Caslant thermostat manufacturer or company: we find the brand at Amazon and elsewhere.

If you have company contact or can give me a copy of the manual pdf, do so via the page bottom CONTACT link and we'll take a closer look

On 2016-04-04 16:41:09.037997 by (mod) -

RE-posting without link (for security)

) Anonymous said:
Can a remote that is designed for Fan Coil Central AC such as this remote [thermostat advertised on Amazon] work with AHU based Central heating and cooling system with Gas Furnace or Heat Pump? The wiring pins at the back seem differently labeled.

Item: Programmable Thermostat,Caslant™ Modern Touchscreen Room 5+1+1 Day Programmable Thermostat Central Air Conditioning Microprocessor-based con LCD Display for Fan Coil Unit(White)

On 2015-12-19 by (mod) -

Disconnect the rhermostat wires at the AC in it end. If it stops, the wires are either shorted together or mis wired

On 2015-12-18 by (mod) -

Manuel

If your AC unit is a heat pump it should be turning on unless outdoor temperatures are so low that only backup heat is to run.

If your AC is not a heat pump but it's turning on when you call for heat I suspect the thermostat is misfired or wires have shorted together.

On 2015-12-18 by manuel a esquivel

theromstat is on heat but ac units turns on why

On 2015-12-18 by Anonymous

Hi, Jeff here. Hv relatively new Trane unit & air handler (elec only, no gas) & tcont800 control. Hv all 7 days programmed the same i.e. w-l-r & s = 78/64 (same settings installer had programmed), fan set on auto & syst set on auto. With that said, right now, It's f'n freezing in here!...current inside temp reading is 67...wtf am i doing wrong? Read manual cover to cover more than once...pretty cut and dry. Thoughts?

On 2015-10-12 by BIP

Just bought a new Trane;both inside air handler and outside compressor. Kept same thermostat rather than replace since it was working fine and in the past some new ones were so bad that we had to reinstall the old one, so I opted to live by the "if it ain't broke don't fix" rule and kept the new one for future use.

The TT has always been accurate but after a week I've noticed that this new system consistently stops as soon as it reaches the set temperature - usually within 5-6 minutes and turns on again within 5- 6 minutes

. If I reset the temp lower by several degrees: ie. 76 to 72, it will delay 90 seconds before both fan and compressor kick in together(a little blinking star on the thermos. indicates when the compressor kicks in) the unit will run until it reaches 72 - about 25 minutes, then stops.

The fan stops along with the compressor where the old unit would continue the fan for about 90 seconds. After reaching the target temp. however, this new system turns back on every 5 minutes to maintain that target temp. within one degree depending whatever that is after 5 min. I read that's referred to as cycling and that its a power sucker.

What can the installer AC co. do to add the 90 second delay in the fan turning *off - not just on - can the range of the target temp be increased from 1-2 degrees to 1-3;

would that limit the wear and tear on the compressor and not bloat my electric bill? How else can I assess whether they installed too big of a compressor? - Both the old and new were 3 ton but the old was much smaller in physical size..

On 2015-09-15 by Wayne

Can you tell me where I can find out how to set program on a 2014 wildcat RV thermostat brand dometic

On 2015-09-14 by (mod) -

Thanks Mr. Ramirez;

Find our email at the page bottom CONTACT link if you're a professional working in the field who wants to be identified.

On 2015-09-13 by hmramirezus@yahoo.com

the reason for the jumper is that your system uses one transformer for heating and cooling. there are systems that use individuals transformers, one for heating and the other one for cooling.

On 2015-09-06 by Bill Honeywell Chrono III thermostat running a lennox furnace and trane ac.

I have a Honeywell Chrono III thermostat running a lennox furnace and trane ac. The thermostat four wire is W G Y R& RC jumped together.

The Lennox connection is W G Y R. C is used for R & C as connection only. The issue is that all functions work correctly except that when trying to run the Fan only (Fan ON) the AC compressor also turns on. Why are R and RC jumped at the thermostat?

...

Continue reading at THERMOSTAT DIAGNOSTIC GUIDE or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see THERMOSTATS, DIAGNOSTIC FAQs-4 - more-recent thermostat troubleshooting questions and answers

Or see these

Recommended Articles

• THERMOSTATS, HEATING / COOLING
• THERMOSTAT SETTING INSTRUCTIONS - Separate article - How to Set the Thermostat
• THERMOSTAT TROUBLESHOOTING - What to check if a thermostat is just not working
• THERMOSTAT WIRE CONNECTIONS - how to wire up all types and brands of heating & cooling thermostats

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THERMOSTATS, DIAGNOSTIC FAQs-3 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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