Things You'll Need
Most furnaces use an igniter and flame sensor to ignite the gas and supply heat to the home. When the igniter fails, the flame sensor will shut the furnace down and cut the gas supply off. This is the reason most furnaces will fail to operate. You can fix an igniter problem on a furnace by replacing the igniter. Once you have a replacement igniter, your furnace will work again.
Turn the power off to the furnace by turning the emergency switch to the off position. The emergency switch is on the wall near the furnace and resembles a normal light switch. It is red.
Open the burner access door by lifting up on the door handle and pulling the door away from the furnace. The igniter will be next to the burner assembly and the flame sensor.
Disconnect the wiring harness from the igniter. Press in on the wiring harness locking tabs with your fingers to separate the harness from the igniter wires.
Use a nut driver to remove the two hex head screws that secure the igniter to the furnace. Pull the igniter out of the furnace. Inspect the porcelain part of the igniter that sits inside the furnace for damage. A cracked or badly discolored igniter tip indicates a faulty igniter.
Take the igniter with you to a HVAC repair facility or HVAC dealer to purchase a replacement. The old igniter will have a model number stamped on the side of the part.
Set the igniter tip inside the furnace and secure the igniter to the furnace using the retaining screws. Do not touch the porcelain igniter tip with your hands. The natural skin oils will shorten the life of the igniter.
Press the wiring harness back into the igniter wires until the connector snaps together. Replace the burner access door and turn the emergency switch back to the on position to supply power to the furnace.
Always disconnect power to furnace before attempting repairs.