How to Replace a Thermocouple in a Wall Furnace


A wall furnace thermocouple works the same way as a thermocouple in any gas-fueled appliance. It sends a thermal signal to the main gas valve and tells it to allow just enough gas into the burner to keep the standing pilot light lit. The main difference between a wall furnace thermocouple and any other type is that a regular thermocouple is screwed into the main gas valve, but a wall furnace thermocouple is directly wired in.

Things You'll Need

  • Screwdriver
  • New thermocouple
  • Turn off the electrical breaker and the gas valve to the wall furnace before you begin to replace the thermocouple.

  • Remove the front panel of your wall furnace with your screwdriver. Most panels will have screws holding them in, but some front panels may have gravity clips, so you can grasp the panel sides and lift them straight up and off.

  • Locate the thermocouple on your wall furnace. It will be in a round mounting hole directly beneath the burner.

  • Pull the thermocouple out of the mounting hole. In most cases, the thermocouple is held in by friction, so it can be grasped tightly and pulled directly out. In some cases, a small set screw may hold it in. If that is the case, remove the set screw first, and then pull the thermocouple out.

  • Trace back the tube connected to the thermocouple. It will end in a pair of colored wires that are connected to electrical posts on the wall furnace. Unscrew these electrical posts and remove the wires, but remember which wire went to what post.

  • Unwrap the new thermocouple and match the colored wires to the electrical posts to which the old one was attached. The colored wires must be attached to the same posts in the same way.

  • Screw the wires to their appropriate electrical connections, then firmly push the new thermocouple into the mounting hole beneath the burner. Flip the breaker to the "on" position, turn on the gas valve, and light the pilot per your specific model's recommendations.

Tips & Warnings

  • When taking the wires off the electrical connections, place a piece of tape over one of the connectors, and then use a marking pen to label which colored wire came off that specific post.

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