We have a Honeywell T8400C1024 Thermostat. It keeps cutting off and tripping the breaker.

What is model of the Thermostat


Did you check the Circuit Breakers to make certain you have not simply tripped a breaker?

In general, depending on where you live: If you will need Heat select Heat then set the desired Temperature
If you will need Cooling select Cool and then set the desired Temperature.
Fan should be set on Auto.

Look at the bottom. If no screws, it's a matter of gently grabbing the bottom of the cover and pull towards you and up. This will release the tabs. Good luck!

Makes sure the thermostat switch is turned to A/C or Cool

Then make sure any switch on the AC unit is turned on

then check the circuit breaker box to make sure your AC breaker did not trip (or may have been turned off by a service technician last fall).

Hello,If just installed the thermostat check that the wires are not touching anywhere.If not the case you have a open(tripped) HIGH LIMIT at the furnace and the blower will continue to run untill it is reset.

This thermostat has batteries. Try replacing the batteries. You may have to reprogram and make sure it is on.

Could be the batteries in the thermostat.

site shows this thermostat is a non programmable unit and has been discontinued. none of the info sheets including a pdf shows a replacement battery. this thermostat operates off line voltage only. check for a control fuse or breaker on your heating unit.

I had this problem once in an apartment I own. it was an EXTREMELY ease fix. my problem as that the set screws in the breakers were not tightened enough, and would cause heat to build up, and trip the breakers. so..... first try to tighten the set screws on your breakers.

The thermostat is a low voltage circuit (24 volts) most of the newer heating systems have a fuse for the low voltage controls. If you are having to re-set the high voltage circuit breaker, then you have something else wrong. When does the breaker trip? while its running or after it shuts off?