How to Replace Ignitions in Furnaces

Shut off the furnace at the thermostat control, usually on a wall in a central location in the building.

Cut power to the furnace at the circuit breaker or pull the fuse from the fuse box.

Close the valve in the gas line attached to the furnace, turning the knob clockwise. The furnace must cool to room temperature before proceeding.

Unscrew and remove the service panel on the side of the unit, near the bottom. The modular ignition system is located between the gas valve and the pilot, which is a tube bent at a right angle. The modular ignition system consists of a flat wire in a housing attached to two wires that connect with a plug on the opposite end.

Grab the plug wired to the back of the igniter with needle-nose pliers and pull it away from the igniter to disconnect.

Remove the screws holding the igniter cylinder to the support bracket. Slide out the igniter in the direction of the power socket from which the igniter was unplugged in Step 5 and remove from the furnace.

Insert the new igniter into the support bracket, holding the igniter by the housing, not the tip. Do not touch any part of the tip.

Tighten the screws in the support bracket to hold the new part in place.

Connect the plug on the back of the igniter to the electrical socket. Push it in by hand.

Fasten the service panel with the screws and screwdriver.

Turn on the power and open the gas valve.

Set the thermostat to the "On" position.