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How to change the battery on my thermostat Honeywell t8001c

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The battery is inside the thermostat. There should be screws / or / it will just pry off the mounting base (not the wall). There are usually rechargable batteries inside.

Posted on Apr 28, 2008


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Posted on Jan 02, 2017


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How do I change the battery on Honeywell Thermostat T8001C?

According to the manual for the model series (see link), only the T8002 Model has batteries. They are accessed from the right side of the thermostat. See page 14.

Jan 10, 2015 | Honeywell T8001C1019 Programmable...

1 Answer

My Honeywell T8001C doesn't allow me to change the indefinite temperature hold for some reason

It sounds like the thermostat is malfunctioning; the Set should not be flashing at all, only the Hld should show after pushing the hold button.
Do you have a new battery in the unit? Is it set to Heat or Cool? Is it already programmed for current Time/Date and does it have a schedule programmed in already? If you've lost the user manual it's here:

Jul 06, 2014 | Honeywell Programmable Thermostat Heater

1 Answer

Power company had to shut power off to my community. When power came back on several hours later its still a blank display and does not work. I have turned off and on every circuit breaker I have in my...

cefb7e0c-979f-4b1a-bff6-c84fcbc4c9cf.pngYou will need a meter and test for 24 volts at red and common, if present, you next need to check at yellow and common and green and common, green being fan and yellow being ac outside.
I suspect the transformer is not providing the 24 volt control power to the stat either due to the high voltage or a low voltage fuse has blown on the board usually a 3 amp auto type, beyond this I am unable to offer much help .

Aug 25, 2013 | Honeywell Programmable Thermostat Heater

1 Answer

I need my t8001c Honeywell to turn the heat on and stay on. Its getting stuck on a hold position but then it goes to away or leave and it wont stay on. I have several manuals for this t8001c and they all...

You are setting the temperature on temporary hold. It stays there until it reaches the time of the next programmed sequence which is away or leave and it jumps back on the program. If you want it to stay all the time where you set it you can push the setting up to the desired temp and push hold. It will stay there permanently until you push run which will put it back on the program if you want. Or just push set and program the whole sequence the way you want then press run.

Jan 11, 2018 | Honeywell Programmable Thermostat Heater

1 Answer

My 9 year old Honeywell T8001C has no display. My FAU AC power breaker is not tripped. I tried a new Honeywell RTH2510B and a RTH7500D but the Fan does not come on with either of the new units after...

This is why battery powered tstats are misleading. The battery provides the power to the tstat but your unit is not providing low voltage in order to run. Air conditioners are controlled by relays and contactors. This means your unit constantly has high voltage going to it but each component runs through a relay in order to turn on. These relays are energized by the low voltage that runs through your tstat. Your tstat is not getting this low voltage. Either your float switch on your drain line is tripped, your blade style fuse is blown on the secondary side of the transformer or your transformer is bad.

Aug 08, 2017 | Honeywell Heating & Cooling

1 Answer

Have the honeywell t8001c thermostat - no batteries - it holds the programming fine but not the date/time - what to do?

Go to
Under red welcome sign
Bottom red highlighted box literature/image search
Type in thermostat model number
Click on arrow to right
Then click on the PDF files owners manual / installation instructions
If you can’t find what you want, the bottom left and bottom of web
Page, they have homeowners assistance and Home products to get the help you need.

Mar 06, 2010 | Honeywell Programmable Thermostat Heater

2 Answers

Battery backup?

which model do you have ? the 8000/8001 or 8011 the set is different depending on your type of heating system. This model has a memory chip not a battery that saves your settings. So you could be looking at replacing the unit.

Jan 05, 2008 | Honeywell Programmable Thermostat Heater

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