How to Replace the Automatic Ignition System in a Furnace

Shut down the furnace both at the thermostat, typically wall-mounted on a control panel, and at the circuit breaker that provides electricity for the ignition system. Wait for the unit to cool.

Remove the bolts holding the cover plate to the bottom side of the furnace using the nut driver. The ignitor is next to the gas valve. Depending on your model, the ignitor will either resemble a ceramic tube with wires on one end and an electrode on the other or a flat, fork-like terminal mounted in a housing with two wires at the back.

Unplug the wires on the back of the igniter from the electrical socket inside the furnace. The wires are connected to a small power cube that fits in the socket. Pull the cube, not the wires.

Loosen the screw or screws in the bracket holding the ignitor housing in position next to the valve. On some furnace models, you'll need to use pliers to loosen and remove a threaded nut holding the ceramic-type ignitor securely in a hole in the bracket.

Remove the old ignition system. Take it with you to an HVAC shop for a replacement or purchase the part from the furnace manufacturer.

Insert the new part in the bracket in the same position as the old part. Tighten the screws or the threaded nut, depending on your model, to secure the new part.

Plug in the wires on the back of the part to the socket inside the furnace.

Fasten the cover plate onto the side of the furnace cabinet with the bolts and nut driver.

Switch on the circuit breaker and turn on the unit at the wall thermostat.