How to Replace the Ignition Harness on a Furnace

A modern gas furnace has an ignition system that lights the burners. The ignition system consists of a glowing metal tip on one end and a power plug on the other. They're attached with a wiring harness. If any part of the ignition system wears out, you must replace the entire module, including the harness. This is a relatively simple repair since the harness is pre-wired to the igniter and the power plug. Buy a replacement ignition harness for your particular furnace model from an HVAC supply shop.

Screwdriver set

Instructions

- 1
  Switch off the furnace at the circuit breaker and wait until the unit cools to room temperature.
- 2
  Turn the gas valve handle on the back of the furnace 90 degrees clockwise to shut off the fuel while you complete the repair.
- 3
  Take out the screws in the service cover, using a screwdriver, to remove the cover. The ignition harness is positioned in between the furnace pilot and the fuel valve. The igniter has a flat, pointed tip on one end, a ceramic or metal housing in the center and a wiring harness from the back of the part to an electrical plug.
- 4
  Grip the electrical plug with your thumb and forefinger, and pull it from the socket.
- 5
  Unscrew the two screws holding the center of the ignition harness to a support bracket. Lift out the igniter and wiring harness to remove them.
- 6
  Set the housing on the new part into the support bracket and secure it with the two screws.
- 7
  Connect the plug on the wiring harness to the electrical socket inside the furnace.
- 8
  Fasten the service cover to the outside of the furnace with the screws.
- 9
  Open the gas valve and switch on the furnace.

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