Honeywell thermostat blowing fuse [Causes and Fixes]

Are you dealing with a thermostat that keeps on blowing a fuse? In this article, we will discuss the potential causes and fixes for a Honeywell thermostat blowing a fuse.

When your nest or honeywell thermostat keeps on blowing the fuse, this is likely caused by a short between R and C terminals causing the fuse in the furnace control board to blow. While this can be frustrating, a fuse typically blows out to prevent your equipment from costly damage.

How to tell if your Honeywell thermostat has a blown Fuse

To start with, you need to be really sure that the fuse is in fact blown out before you go into investigating what is causing the problem.

Here are a few things to look out for.

Heating and Cooling not turning on

If there is a blown fuse in the control board, you will have problems turning on and off heat and cooling. When you outside ac condenser is nor turning on, you may have a blown fuse on the air handler circuit control board it:

  1. The circuit breakers are not tripped: When the circuit breaker is not tripped, you should have power going to your condenser or indoor unit.
  2. The switch for the furnace is turned on: When both the circuit breaker is on and the furnace switch is also turned on, you should have no reason for the heating/cooling system failing to turn on.
  3. The furnace door is closed: The furnace door has a switch that opens when the door is open. It is important to keep the door alway close to ensure your heating/cooling system is always powered on.

Also read: Honeywell thermostat not showing cool option

Troubleshooting a thermostat that is blowing a fuse

Now let’s look at some of the steps you can take to troubleshoot  and fix this problem. 

Is this a new installation? If so, try reinstalling the old thermostat.

Is your old thermostat working without problems? If so, there could be a problems with the wiring on the new thermostat or your new thermostat could be damaged

To test whether it is your thermostat causing this problem or there is a short between wires;

  • Remove the thermostat from the wall
  •  Use a multimeter to test for continuity. check the resistance between the R and C terminals. If there is no continuity, there could be a bad thermostat. 
  • If there is continuity, go to the furnace and do the same on the R and C wires. If there is no continuity between the two, you may either have a short in thermostat wiring or a short that is caused by placing the thermostat on the wall plate.

How to replace a fuse on control board

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