How to Find a Spark Ignitor on a Furnace

As you turn on a gas furnace thermostat, it sends a signal to light the burners and turn on the blower. This same signal sends electricity to the ignitor to help light the gas in the burners. If your furnace makes clicking noises as it lights, it is equipped with a spark ignitor. The clicking noise you hear is the electric current creating a spark to light the pilot. Once the pilot lights, it then lights the gas supplied to the burner from the manifold. When the spark ignitor fails to initiate a spark, the furnace cannot produce heat.


Shut off the electrical power to your gas furnace. Depending on the installer and the local codes at the time of installation, you may have a disconnect switch next to the furnace. Turn off the breaker to the furnace at your main electrical panel if you do not find a disconnect switch.


Remove the burner compartment door from the front of your furnace. Look for the gas control valve inside the compartment that supplies gas to the burners. Depending on the design of your furnace, the burners could be at the top or the bottom of the burner compartment.


Find the small, metal gas pilot tube attached to the gas control valve. Trace the line until it terminates at one of the gas burners. The gas line connects to a metal burner assembly bracket that holds the pilot tube and the spark ignitor. Some burner assemblies may hold a flame sensor as well. The spark ignitor looks like a 1-inch long metal probe attached to one end of a solid ceramic tube with an electrical wire attached to the other end of the tube. If your furnace had a hot-surface ignitor, it would appear as a flat piece of metal attached to one side of a square piece of ceramic with two wires attached to the other side of the ceramic. Both ignitors are attached at the burners, but the hot-surface ignitor does not use a pilot or have a flame sensor attached to it.