How to Know if your Furnace Ignitor is Bad (7 Step Guide)

Are you having problems with your furnace, and think the furnace ignitor could be causing the issue? You’re in the right place!

If your furnace won’t turn on (or in some cases, the furnace will seem to start working but won’t actually light), won’t blow warm air, starts and stops, or consistently trips breakers in your house, a bad furnace ignitor could be the culprit.

In this guide, you’ll learn

  • What is a furnace ignitor?
  • Supplies you’ll need to check your furnace ignitor
  • What to check before concluding your furnace ignitor is the culprit
  • How to check your furnace ignitor if you have a voltage meter
  • Best way to check your furnace if you don’t have a voltage meter

What is a furnace ignitor?

The furnace ignitor is a small metal piece (that usually looks like two flat prongs) protected by a ceramic casing and connected to the furnace with electrical wires.

It’s responsible for automatically lighting the gas that’s used to heat your home.

A quick note before we proceed: this guide will focus on a specific type of ignitor called a hot surface ignitor. Hot surface ignitors are the focus of this article because they are far and away the most common type of ignitor in modern furnaces.

The good news is that, if you determine your furnace ignitor is behind your furnace malfunction, it’s a relatively cheap and easy repair.

That is to say, if your furnace breaks down, you might find yourself hoping the ignitor is to blame!

Before going through the below steps, it’s important to do the following basic troubleshooting:

  1. Check your thermostat – Ensure your thermostat is set to a temperature higher than the temperature in your home
  1. Check your circuit breaker and furnace power switch (if you have one) – Without the circuit breaker and furnace power switch getting electricity to your furnace, your furnace won’t start

Supplies You’ll Need to Know if your Furnace Ignitor is Bad

  1. Small nut driver (or wrench) – Your ignitor is attached to a bracket that is held in place with screws. We’ll use a small nut driver or small wrench to unscrew this bracket and remove the furnace ignitor.
  2. Angled bit holder – This is used for the same purpose as our nut driver / wrench above, but can make the process of removing your ignitor much easier for certain furnace models. Some newer, high efficiency furnaces house the ignitor in hard-to-reach places in the furnace, so an angled bit holder can be your best friend.
  3. Meter – The meter is used to test whether power is getting to your ignitor. There are less direct ways to conclude your furnace ignitor is bad, but using a meter is the only way to know for sure. You’ll want either a voltage meter or a multimeter that can check both voltage and resistance (ohms).

How To Know if your Furnace Ignitor is Bad (7 Steps)

Step 1: Turn off all power to the furnace

Safety first! Before inspecting your furnace ignitor, be sure first the power to your furnace is off (and make sure your furnace power switch is off, if you have one – this typically looks like a small light switch on the outside of your furnace).

Step 2: Remove the Furnace Doors

Different furnace doors come of in different ways. Some are spring-loaded and slide off, while some have screws or knobs.

Step 3: Return power to the furnace

Once the access panels are removed, returning power to the furnace will let you observe (via sight and sound) what is happening with your furnace. At this time, there are a few questions you should ask yourself:

Note: be careful not to touch the furnace with the power turned on

  1. Does the inducer motor turn on?
    • Once you return power to the furnace, if the thermostat is set to call for heat, your inducer motor should turn on within about 10 seconds. The inducer motor is a motor-driven fan inside a metal case, and you will hear the fan blowing.

  2. Does the gas valve open?
    • Another 10 – 20 seconds after the inducer motor turns on, you should hear a loud “click”, which indicates the gas valve has opened (you have likely heard this click in your home in the past).

  3. Is the gas running?
    • Shortly after the gas valve opens, you should be able to hear the gas working its way through your furnace (you’ll usually a hissing sound).

  4. Is the furnace ignitor heating up?
    • When working properly, the ignitor will start to glow a shade of orange

If your answer is “no” to any of questions 1, 2 or 3 above, your ignitor is likely not the cause of your furnace not working. Note, the furnace ignitor will not heat up in this instance. Nevertheless, we’ve already determined the cause of the problem is elsewhere.

If the answer to each of questions 1, 2, 3 and 4 above is “yes”, then your furnace ignitor is likely not the cause of your furnace not working.

If the answer to each of questions 1, 2, and 3 is “yes”, but your ignitor is not heating up, then your ignitor could be the cause of your faulty furnace. Turn the power to your furnace off and move on to the next step.

Step 4: Disconnect your furnace ignitor from your furnace

This step simply involves disconnecting the wiring that runs from your furnace to the furnace ignitor. For hot furnace ignitors, there are typically two wires attached to a connector. to Be sure the power to the furnace is off before tampering with any wiring.

Step 5: Test your furnace ignitor with your meter

Once the ignitor is disconnected, turn the furnace power back on. The first thing to test is the voltage going to your ignitor. Set your meter to its volts setting and gently place the meter leads inside the plug you just disconnected from the ignitor.

Do not force your leads inside the plug, as this could damage the connectors.

You should see approximately 120 volts coming to your meter.

If you see ~120 volts in your meter, and everything else in your furnace is working properly, that’s a good indicator that your furnace ignitor is likely causing the problem. Turn the power off and proceed to step 6

Step 6: Remove your furnace ignitor

With the power turned off, use your nut driver / small wrench (or angled bit holder if necessary) and unscrew the ignitor bracket from the furnace.

Note: the ignitor itself is fragile. Be careful when performing this step not to bump the ignitor against the furnace or otherwise apply pressure to the ignitor.

Similarly, do not touch the ignitor itself (meaning the metal) with your bare hands. The oil on your hands will transfer to the ignitor, which is bad for the ignitor and will cause it to wear down very easily if put back in the furnace.

You can freely touch the ceramic casing and metal bracket.

Step 7: Visually Inspect the furnace ignitor

Take a good look at the furnace ignitor itself. Does it have either a crack, or white streaks running across it? If so, these are signs that your furnace ignitor is in fact bad and needs to be replaced.

Stephen Marks

Stephen Marks

Stephen is an HVAC and home-repair enthusiast. He's here to answer any of your questions about HVAC!

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Stephen Marks

Stephen Marks

Stephen is an HVAC and home-repair enthusiast. He's here to answer any of your questions about HVAC!

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