How To Test The Ignitor For A Furnace That Isn’t Heating

Older models of gas furnaces had a pilot light that signaled when the furnace needed more gas to burn for the heating process. An electrical ignitor is typically more reliable than older model pilot lights but, like any electrical device, the ignitor can still malfunction or stop working over time. If your furnace has stopped heating completely, it's possible that your ignitor has a problem.

You can test the ignitor's functionality by using a multi-meter to check for continuity, or the continuous flow of electricity through the ignitor. This testing tutorial assumes you have already removed the ignitor from the furnace or that you have isolated the ignitor within the furnace for easier testing. Consult your owner's manual for instructions if you still need to remove the ignitor.

What You Need:

  • Ignitor
  • Multi-meter with ohms setting
  • Owner's manual
  • New ignitor

Step 1: Testing the Ignitor

Set your multi-meter to the lowest setting possible for the ohms reading. Position your ignitor so that the filament is pointing away from you and the plug portion is pointing towards you. Note that you do not want to touch the filament as that could break the ignitor, which you have yet to test for functionality. You don't want to break a working ignitor trying to test it.

The plug part of the ignitor should have two connection points or terminals that correspond to the two probes on your multi-meter. Attach one probe to the first terminal and the other probe to the second terminal.

Step 2: Checking the Reading

Consult your owner's manual for the ideal ohms range for your unit's ignitor. If that number is met on the reading on the multi-meter, then your ignitor is in working order and the problem might be elsewhere in the unit. Replace the ignitor you currently have and call in a heating repair service for assistance.

If your multi-meter doesn't show a reading at all, then your ignitor is broken and you will need a replacement piece. If the reading barely goes up, then your ignitor is likely failing and needs replaced. Purchase a replacement piece through a specialty retailer or the manufacturer and follow the installation instructions to place the new ignitor. Restore power to your unit and then test to make sure the new ignitor works.

If your unit is still behaving oddly, call in a heating and cooling service tech, such as Thermotech Inc, for deeper diagnosis and repairs.