Well, you’ve just discovered your thermostat’s shot. As a furnace owner, you need to know exactly what to do, without any unnecessary delays. Let’s get to it then.

When replacing the thermostat, make sure the new one has exactly the same voltage rating. After all, it has to be compatible with your furnace. Here’s how the replacement process works:

  • First, unplug the furnace from the outlet or tune the breaker to the furnace. If bare wires touch you may burn up a transformer.
  • To remove the old thermostat, take the faceplate off of it and locate the mounting screws. Remove these, and it’s now free from the wall. Remove wires from the back of your old part by turning the connection screws counterclockwise. Be careful here: we don’t want any loose wires falling down between walls.
  • Clean the exposed wires; scrape them with a utility knife to make the wires’ ends shine. Attach the wires to your new thermostat. Just to remind you, the electrical/voltage rating needs to match.
  • Next, push the wires into the back of the wall and tape up the opening to prevent cold air from seeping through. If it isn’t sealed properly, it will definitely affect the efficiency of your thermostat.
  • Now you need to put back the mounting screws to attach the new thermostat to your wall. If the thermostat has a mercury tube, the unit needs to be completely leveled during installation. Mercury tube thermostats tend not to function accurately unless they’re completely level.
  • Put the faceplate back where it needs to be. Ensure the new thermostat switches your heating system on and off as the temperature is adjusted.
  • Reconnect power.

Follow these simple steps and rest assured, when the time comes, you can easily replace the thermostat yourself.

Once you replace your furnace thermostat, if you need help programming it clicks here –

This article was provided by American AC Heat Plumbing. Since 1981, American Air has been providing professional air conditioning and heating service and repair. Check out their $99 furnace tune-up special!


James Smith

As you can tell from our humble beginnings in 1981, we began as a family-owned business and stayed a locally owned air conditioning and heating company in Los Angeles county for nearly 40 years.