Back Button

How to Troubleshoot a Honeywell T8000c Thermostat

Robert Vaux

Honeywell T8000c thermostats are designed to be simple and trouble-free. The control panel is extremely straightforward and its no-nonsense operation emphasizes longevity over a lot of bells and whistles.

But like any other piece of equipment, it can break down, and if there's something wrong with it, then calling in an expert or replacing it with a new one may be necessary. Before you do that, however, perform a few basic troubleshooting steps: that may coorect the problem without spending any additional money.

  1. Check the circuit breaker to the part of the house which includes the T8000c thermostat. If it has been tripped, the thermostat isn't receiving power. This may be the culprit if the control display won't turn on, or no air is blowing to heat or cool the house.

  2. If you can't set the thermostat below 40 degrees or above 99 degrees Fahrenheit, don't panic. The T8000c wasn't designed to raise or lower the temperature beyond those parameters. Move the temperature gauge to a number between 40 degrees and 99 degrees, and the thermostat should work just fine.

  3. Wait. It may take as long as five minutes for the thermostat to begin heating or cooling the house. Nothing is wrong; it simply takes that long to bring the various components up to the proper temperature. Pay particular attention to this if the little flame sign or snowflake sign is flashing. The T8000c has a minimum-off timer--which lasts two minutes--indicated by those flashes. If the thermostat still isn't running after a full five minutes, there may be something else wrong.

  4. Make sure the "System" switch is specifically set to "Heat" or "Cool." The thermostat won't run the A/C when it is set to "Heat" and won't run the heater when it is set to "Cool."

  5. Double check to make sure the thermostat is firmly connected to the wall mount, with the latches snapped shut. It won't work unless it is.

  6. If you have just installed the thermostat, double-check the wiring to make sure each wire is connected to the proper terminal. The terminals all have a letter code, which should correspond to the terminals on the older thermostat. It's a good idea to label the wires when you are installing the T8000c to ensure you don't plug one into the wrong terminal.

  7. Turn the thermostat on. It may sound obvious, but you may have inadvertently switched the thermostat to the "off" position while performing another function. Better to double check and feel foolish than call a repairman and have a witness to it.


Honeywell offers a warranty for one year after the purchase of a T8000c. If troubleshooting doesn't correct the problem and the warranty is still in effect, consider contacting Honeywell and asking for a replacement. Instructions can be found in your T8000c owner's manual.