Furnace Ignitor Replacement

How do I tell if my furnace ignitor is bad?

The clearest sign of a bad ignitor is the furnace going through its full startup sequence but never lighting: you hear the inducer motor spin up, you may hear the gas valve click, but the burners never catch and the furnace either blows cold air or shuts down on a safety lockout. Many furnaces will try two or three times, then stop and flash an error code on the control board behind the access panel. A code that points to ignition failure or a failed ignitor is a strong tip.

A healthy hot surface ignitor glows bright orange within a few seconds of the call for heat. If you watch through the sight window without removing panels and see no glow at all, the ignitor is a prime suspect. Cracked ignitors often look intact to the naked eye, so the absence of a glow matters more than how it looks. Short cycling, where the furnace fires briefly then quits and retries, can also be ignition-related, though that symptom overlaps with a dirty flame sensor (more on that below).

Before you blame the ignitor, rule out the simple stuff: a tripped furnace switch, a blown fuse on the control board, a clogged filter triggering a limit-switch shutdown, or a thermostat set wrong. Our why is my AC or furnace not working guide walks the full no-heat checklist in order so you do not replace a $30 part when the real fault was a flipped switch.

What causes a furnace ignitor to fail?

Furnace ignitors fail mostly from thermal stress. The element heats to well over 1,800 degrees and cools again every single cycle, sometimes dozens of times a day in cold weather, and that constant expansion and contraction eventually cracks the brittle ceramic. This is normal wear, not abuse, which is why ignitors are treated as a consumable part rather than a permanent one.

Two other things shorten their life. Touching the element with bare fingers leaves oils that create hot spots and early cracking, which is why techs handle a new ignitor by its ceramic base only. And voltage spikes or a furnace that short cycles put extra heating cycles and electrical stress on the element. A furnace that keeps eating ignitors every season usually has an underlying problem, like restricted airflow or a control issue, that is worth diagnosing rather than just swapping the part again.

There are two materials. Silicon carbide ignitors are the older, fragile, flat or spiral type and typically last 3 to 5 years. Newer silicon nitride ignitors are sturdier and often last 7 years or more. If your furnace keeps burning through the old-style part, upgrading to a quality silicon nitride replacement (matched to your furnace) is usually the better long-term choice.

How much does furnace ignitor replacement cost?

Expect $150 to $300 for a professional furnace ignitor replacement, including the part, the service call, and labor. The ignitor itself is inexpensive, usually $15 to $50 for a universal or model-specific hot surface ignitor, so most of the bill is the trip charge and diagnostic time. After-hours or emergency calls during a cold snap push the total toward $350 to $450.

That range is for the ignitor alone. If the tech finds the ignitor failed because of another fault, like a cracked heat exchanger, a bad control board, or a failing inducer motor, those repairs are priced separately and cost considerably more. Bundling the fix into an annual tune-up, which runs about $80 to $200 on its own, often saves money because the diagnostic and trip charge overlap. See our furnace maintenance checklist for what that visit should cover.

If your furnace is more than 15 years old and the ignitor is one of several failing parts, weigh the repair against replacement. A string of repairs on an aging gas furnace can signal it is time to plan a new system; our heat pump vs furnace comparison is a useful read before you spend, and the BTU calculator helps you ground what size system your home actually needs.

Can I replace a furnace ignitor myself?

Mechanically the ignitor is a simple plug-in part held by one or two screws, so it looks like an easy swap, but it sits in the burner area of a gas appliance, and that changes the risk math. Always cut power at the furnace switch or the breaker before opening any panel, and never handle the new element by anything but its ceramic base. The element is brittle enough to crack from a fingernail tap, and a hairline crack you cannot see will leave you back at square one.

The bigger hazard is not the electricity, it is the gas. A loose, mis-aligned, or weak ignitor that lights the burners a beat too late causes a delayed ignition, where gas pools and then lights in a small puff or rollout. Done repeatedly that can damage the furnace and, worst case, push combustion gases where they do not belong. This is exactly why we do not publish a step-by-step ignitor procedure: getting the position and seating right, and confirming clean ignition afterward, is what you are paying a tech to verify.

Our honest take: if you are an experienced DIYer who is genuinely comfortable working around gas equipment, the part is straightforward. For everyone else, the $150 to $300 a pro charges buys a correct diagnosis, the right part, and a verified clean light-off, which is cheap insurance on a gas appliance. If you smell gas at any point, leave and call your gas utility, not an HVAC tech.

Furnace ignitor vs flame sensor: what is the difference?

These two parts get blamed for each other constantly because both cause no-heat and short-cycling symptoms. The ignitor lights the gas; the flame sensor confirms the flame is actually burning. The ignitor glows orange and fires the burners. A few seconds later the flame sensor, a thin metal rod sitting in the flame, tells the control board it can keep the gas valve open. If the sensor does not detect flame, the board shuts the gas off as a safety measure.

The telltale difference: a bad ignitor means the burners never light, while a dirty flame sensor lets them light and then shut off after a few seconds, often repeating in a frustrating loop. A flame sensor is usually just dirty rather than broken, and cleaning it is a far simpler and cheaper fix than an ignitor. If your furnace lights and dies in a rhythm, suspect the flame sensor first; if it never lights at all, suspect the ignitor.

How long should a furnace ignitor last?

A furnace ignitor typically lasts 3 to 7 years, with the older silicon carbide type at the low end and the newer silicon nitride type at the high end. That is shorter than most furnace parts, so an ignitor failing once over a furnace's life is normal and not a sign the furnace is failing.

You can stretch its life a little. Keeping the filter clean and the airflow unrestricted prevents the limit-switch shutdowns and short cycling that pile on extra heating cycles. A surge protector on the furnace circuit helps against voltage spikes. And during the annual tune-up, ask the tech to check the ignitor's resistance and the flame sensor; catching a weak ignitor in early fall is a lot better than discovering it on the first hard freeze.

Frequently asked questions