How to Tell if an Ignitor on a Gas Furnace Is Working

The ignitor is inside an access plate at the bottom of the furnace.

A modern gas furnace works with an ignitor to direct a spark over the gas valve for lighting the burner. When you adjust the thermostat control for your heating system to a higher temperature, the thermostat sends a signal to the furnace. The signal passes through a relay switch that directs voltage to the ignitor. If your furnace cuts off intermittently, the problem may be traced to the ignitor. Use a multimeter to test the voltage.

Things You'll Need

• Screwdriver
• Multimeter

Instructions

1. Dial the thermostat control as low as possible and turn off the furnace at the control panel, which is typically done by pushing a slide switch.

2. Unscrew the square or rectangular access plate near the bottom of the furnace to locate the gas valve and ignitor. The ignitor is an L-shaped wire coated in ceramic material similar in appearance to a spark plug.

3. Follow the two wires from the ignitor to the connector plug and remove the plug from the socket.

4. Set the multimeter to read voltage and attach the two probes on the device to the two wire prongs where the ignitor plug was connected.

5. Turn on the furnace and raise the temperature control to activate the furnace relay switch, which produces a clicking sound. Check the multimeter when you hear the click. If the multimeter reads higher than 110 volts the ignitor is bad.

References

• Chicago Heater: Testing an Ignitor on a Furnace
• HVAC for Beginners: Furnace Troubleshooting