How To Check If A Furnace Ignitor Is Bad? A Complete Guide

Rima Chatterjee


Troubleshooting a furnace issue? A faulty ignitor could be the cause. As an experienced HVAC technician, I’ve seen this issue many times. Don’t fret, you can deal with this dangerous problem safely.

Signs of a bad ignitor are heat failing to generate, pilot light won’t light, and cold air blowing from vents. If any of these occur, check if the ignitor is faulty.

To test for voltage at the ignitor, turn off power to furnace via circuit breaker. Wait for it to cool, then access panel and wiring. Look for wires connecting furnace control board to ignitor (spark or hot surface). With multimeter set on volts AC, test each side of connection. If nothing shows, faulty ignitor.

Inspect with emery cloth and magnifying glass if needed. Extensive damage means you need a new module rather than cleaning debris from plates.

If you’re unsure of DIY repair skills, call an HVAC contractor before someone tries repairs with no experience. Watch out for these warning signs before it’s too late.

How To Check If A Furnace Ignitor Is Bad

Image of a furnace ignitor of a furnace

Warning Signs of a Bad Furnace Ignitor

Furnace ignitor problems can be dangerous. 

Here are warning signs to watch out for:

  • The furnace won’t turn on? No heat?
  • Constant cycling?
  • Pilot light out?
  • No heat from vents?
  • Intermittent heating?
  • Gas leaks?

If you spot any of these issues, it’s best to act now. Inspect wiring and plugs. Try DIY multimeter testing. Still don’t know what to do? Call an HVAC technician.

Also, remember to maintain your furnace. Regular maintenance and air filter replacements can help avoid problems. Check the furnace ignitor regularly to stay safe.

Troubleshooting a Faulty Furnace Ignitor

When your furnace ignitor won’t start the combustion process, you may face a chilly day without heat in your home. 

Here’s a four-step guide to troubleshooting a faulty furnace ignitor.

  1. Check the circuit breaker: If your system isn’t heating but the fan is on, see if the circuit breaker has tripped. Flip it back and see if it solves the issue.
  2. Check the room temperature: If it’s too low and no hot air comes out of vents when you raise the thermostat, there may be an issue with your ignitor.
  3. Inspect the igniter: Check for physical damage or cracks on the multimeter wires of an old furnace ignitor. If everything looks fine, use a multi-meter to determine if an electric current is flowing.
  4. Test the voltage signal: Test the voltage signal across HSI or Hot Surface Ignitors using a voltmeter according to the manufacturer’s instructions, typically around 120 volts AC.

Now, let’s look at what else we can do. Pilot flame or spark ignitors, direct spark ignitors (DSI), and hot surface ignition (HSI) can wear out over time and fail due to corrosion or other causes. Furnace repair needs an experienced HVAC technician.

My friend once had their furnace producing little heat, even after changing air filters. Fall was here and it was getting chilly. It turned out that one of the prongs connecting the furnace’s burner had disconnected, leading to cold rooms instead of heated ones. Always take warning signs seriously when something’s wrong, and don’t hesitate to get help if you need it!

Time to spark up some DIY skills and replace that bad furnace ignitor before the cold air forces you into hibernation.

Replacing a Bad Furnace Ignitor

Replacing a bad furnace ignitor can be tricky. 

But, with this 6-step guide, it can be done easily.

  1. Turn off the power. Before starting any work on your furnace, make sure to turn off the power supply at the circuit breaker or breaker box. This will prevent any electrical accidents.
  2. Remove the panel and disconnect the wires. Take off the front panel and locate the ignitor. Then, disconnect the wires from both ends of the faulty furnace ignitor.
  3. Remove damaged part. Use screws or bolts to free the faulty furnace ignitor. If it’s stuck, try cleaning its prongs and base connection with an emery cloth.
  4. Install new ignitor. Reverse the steps above to put a new ignitor in place.
  5. Test spark or hot surface ignition. Depending on the model, you may have a spark or hot surface ignition system. These systems require different setups and testing methods.
  6. Restore power. Connect everything back together, like wiring and panels. Then, turn on the power supply at the circuit breaker and switch on the heating system via the thermostat.

If you notice signs of cold air blowing out of the vents, even though the temperature is set correctly, or hear unusual sounds like banging or clicking, and nothing comes out of the heater, it’s time to call an HVAC technician.

Once I had invited some guests over for dinner during winter and my furnace started behaving strangely, like not heating properly. I called my contractor, who saved me from disaster. He identified one small flame indicating a pressure switch, which was quickly fixed, instead of leaving the situation to unknown faults.

Keep your furnace ignitor happy and you’ll stay warm all winter, here are my top pro tips for maintaining your system:

Pro Tips for Maintaining Furnace Ignitors

Maintaining your furnace ignitor is key. 

Here are some pro tips to keep it in check:

  • Replace your air filter regularly to stop debris from blocking the ignitor.
  • Check the pilot flame now and then. If there’s no spark when it starts up, the pilot light might be the culprit.
  • If you think there’s a problem, use a multimeter to test the voltage. A lower than 30 volts means a bad ignitor.
  • If you need to change the ignitor, buy the right one for your furnace model. Follow instructions carefully.

Stay alert for signs of a faulty ignitor. If the furnace cycles too much or produces cold air, there could be an issue.

Don’t wait for gas leaks or combustion problems to call in a technician. Keep an eye out for warning signs and prioritize maintenance to stay safe and save money. Become an ignitor detective and sort out any heating issues in your home.


Troubleshooting your furnace ignitor might have revealed it is faulty. Ignitor troubles are common. They can make your furnace stop working or cycle on and off. Replacing the ignitor should fix the issue. Ensure the new ignitor matches your furnace model. Handling furnace repairs can be dangerous, so call a professional if you’re not comfortable doing it yourself. When inspecting an ignitor on a gas furnace, check for debris buildup or damage on both ends. If your furnace lights up but doesn’t stay on, or if there’s no hot air for a long time, it might be a bad ignitor. One homeowner had their furnace cycling on and off frequently, then it stopped working. After checking the breaker box and thermostat wiring connection, the ignitor was found as the problem.

About the author

Debarghya Roy: A heating systems author, Passionate about energy efficiency and sustainability, Sharing insights and empowering readers through informative blog articles.