A furnace that starts, pauses, tries again, and then shuts down can make you wonder whether its ignitor is on the way out. Sometimes it is. But a failed start can also come from a dirty flame sensor, an airflow problem, or another part of the furnace, so replacing the ignitor based on one symptom can waste money. Here’s how to tell when replacement is likely, what affects an ignitor’s lifespan, and when it’s safer to call a heating professional.
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When should a furnace ignitor be replaced?
Replace a furnace ignitor when it’s cracked or visibly damaged, when testing confirms it no longer works within the manufacturer’s specifications, or when a qualified technician identifies it as the cause of repeated ignition failures. There isn’t a universal replacement schedule: an ignitor may last for years, but its life depends on the furnace, the part, and how often the system runs.
In other words, don’t replace an ignitor just because your furnace is a certain age. Pay attention to how the furnace behaves, and have the fault diagnosed before buying a part. A furnace can fail to light for several reasons that look much alike from the thermostat.
What the furnace ignitor does
In many modern gas furnaces, the ignitor lights the gas when the heating cycle begins. The thermostat calls for heat, and the furnace runs through a safety sequence before opening the gas valve. Depending on the furnace design, the ignitor either heats up until it can light the gas or creates a spark that ignites it.
These are the two common types:
- Hot-surface ignitor: An electrical current heats a small ceramic element until it glows. The furnace then releases gas at the burner, where the hot element ignites it.
- Spark ignitor: An electrode produces a spark near the burner to light the gas. It doesn’t glow like a hot-surface ignitor.
The distinction matters because the parts aren’t interchangeable, and the signs of trouble can differ. Check your furnace manual or have a technician identify the system before ordering a replacement.
Signs your ignitor may need replacing
The ignitor is visibly cracked or broken
A crack in a hot-surface ignitor is a strong reason to replace it. These elements are fragile, and even a small crack can interrupt the electrical path or worsen as the ignitor heats and cools. Don’t touch the element to check it. Oils from your skin can damage some models, and the part can be delicate even when the furnace is off.
A damaged spark electrode also needs attention, but a technician should check its position and wiring as well. A loose connection or incorrect gap may cause ignition trouble that isn’t fixed by replacing the electrode alone.
The furnace attempts to start but never lights
If you hear the furnace begin its startup sequence but it doesn’t light, a faulty ignitor is one possible cause. With a hot-surface model, you might see the ignitor glow without the burners lighting. With a spark model, you might hear repeated clicking without ignition.
Those clues aren’t proof. Gas supply problems, a faulty gas valve, a pressure-switch issue, or a blocked vent can also prevent a successful start. The furnace’s control board may shut down the attempt when a safety check fails, so the order and timing of events matter.
The furnace starts and then shuts off
A furnace that lights briefly and then stops may have an ignitor problem, but a dirty or failing flame sensor is another common possibility. The ignitor starts the flame; the flame sensor checks that a flame is present. If the sensor doesn’t detect it, the furnace may close the gas valve as a safety measure.
That’s why replacing the ignitor without testing can miss the real fault. A technician can read the furnace’s error code and test the relevant components instead of guessing from the symptom alone.
The furnace makes several unsuccessful attempts
Repeated clicking, glowing, or restarting can indicate that the ignition sequence isn’t completing. Some furnaces make a limited number of attempts and then enter a lockout mode. Turning the thermostat off and on may restart the sequence, but repeated resets won’t repair a failing part and can make diagnosis harder.
If the furnace keeps trying and failing, stop resetting it and arrange an inspection. Note what you hear or see during startup, and tell the technician whether the burners light at all. That information can help narrow down the cause.
Symptoms that can point to other problems
Ignition trouble doesn’t automatically mean the ignitor is bad. The furnace depends on several parts working in sequence, and a problem earlier or later in that sequence can look like an ignitor failure.
| What you notice | Possible causes | Why it needs checking |
|---|---|---|
| The ignitor glows, but no flame appears | Gas supply, gas valve, burner, or ignitor position | The ignitor may be working even though gas isn’t reaching the burner correctly. |
| The burners light, then shut off quickly | Flame sensor, airflow, or another safety control | The furnace may be shutting down because it can’t confirm a safe, steady flame. |
| The furnace does nothing after a call for heat | Thermostat, power, door switch, control board, or safety switch | The ignition sequence may not have started at all. |
| You hear clicking but see no ignition | Spark electrode, wiring, gas supply, or control issue | Clicking alone doesn’t show whether the spark is strong or correctly positioned. |
This table is a starting point, not a diagnosis. Furnaces differ, and the same symptom can come from different faults. Error codes and electrical tests are more useful than guesswork.
How long does a furnace ignitor last?
There’s no dependable lifespan that applies to every ignitor. Some last for many heating seasons; others fail sooner. Hot-surface ignitors are particularly fragile, and repeated heating and cooling can stress the element over time. Frequent furnace cycling, a poor electrical connection, or handling the element during installation may also shorten its life.
Because of that variation, routine maintenance should include checking the ignition system, but it doesn’t mean automatically replacing a working ignitor every year. Follow the furnace manufacturer’s maintenance guidance, and replace the part when inspection or testing shows it’s damaged or out of specification.
Can you replace a furnace ignitor yourself?
Some experienced homeowners may be able to replace an accessible hot-surface ignitor, but the work involves electricity, gas-fired equipment, and a fragile, model-specific part. If you’re unsure how to shut off the furnace safely or how to identify the correct replacement, leave the job to a qualified HVAC technician.
If you do any permitted inspection, turn off power to the furnace first and follow the manufacturer’s instructions. Don’t touch the ignitor element, bend an electrode, or bypass a safety switch. The replacement must match the furnace’s specifications and sit in the correct position; a part that looks similar may not be compatible.
After a repair, the furnace should complete its startup sequence and run normally. If it still fails to light, stop troubleshooting and get professional help rather than repeatedly restarting it.
When to call a heating professional
Call an HVAC technician if the ignitor is damaged, the furnace repeatedly fails to light, a reset doesn’t resolve the problem, or you can’t tell whether the furnace is using a hot-surface or spark ignitor. A technician can check the ignitor, flame sensor, wiring, gas supply, venting, and safety controls as part of a proper diagnosis.
If you smell gas, don’t try to relight the furnace or operate electrical switches. Leave the building and contact your gas utility or emergency services from a safe location. Treat a gas smell as a safety issue, not a routine ignitor repair.
How to help an ignitor last longer
- Keep up with furnace maintenance. A routine service visit can catch loose connections, airflow issues, and other faults that interfere with ignition.
- Replace the air filter as recommended. A clogged filter can restrict airflow and contribute to furnace shutdowns, even though it doesn’t directly fix or damage the ignitor.
- Use the correct replacement part. The right model and installation position help the furnace ignite reliably and safely.
- Avoid unnecessary resets. Frequent restarting won’t repair a failing component and can obscure useful clues about the original fault.
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Frequently Asked Questions
Should I replace a furnace ignitor on a schedule?
Usually, no. There’s no single replacement interval that suits every furnace. Have it inspected during maintenance, and replace it if it’s damaged or testing shows it has failed.
Can a furnace ignitor glow and still be bad?
Yes. A glowing ignitor can still be weak, cracked, incorrectly positioned, or unable to ignite the gas reliably. But if it glows and the furnace doesn’t light, the cause could also be elsewhere in the ignition system.
Is a flame sensor the same as an ignitor?
No. The ignitor lights the gas; the flame sensor confirms that a flame is present. A furnace that lights and then shuts down may have a flame-sensor problem rather than a failed ignitor.
Will a furnace run if the ignitor is broken?
In most systems, it won’t produce heat because the gas burners can’t light safely. The furnace may make several attempts and then shut down or enter a lockout state.
Conclusion
Replace a furnace ignitor when it’s visibly damaged or a proper test confirms it has failed—not simply because the furnace is old or has had one bad start. Since a flame sensor, gas supply, wiring, or safety control can cause similar symptoms, diagnosis matters. If the furnace repeatedly fails to ignite or you’re unsure what you’re seeing, have a qualified technician check it.
