My furnace went through three ignitors in four years before I figured out what I was doing wrong. Not with the furnace — with the ignitor itself. Silicon nitride ignitors are brittle in a way that surprises most people the first time they hold one, and I broke my second replacement just setting it down too hard on a metal toolbox. That’s the kind of detail nobody mentions until you’ve lived it.
If your furnace clicks, the blower kicks on, and then nothing lights, the ignitor is the first place to look. It’s a small ceramic or silicon nitride rod that glows white-hot to ignite the gas, and it fails more often than almost any other furnace part because it’s doing the most physically demanding job in the system, over and over, for years. The good news is that replacing one is a genuinely approachable DIY repair. The part itself usually runs $20 to $60, and the job takes most people under an hour once they know where to look.
Confirming the Ignitor Is Actually the Problem
Before you buy a part, it’s worth ruling out the obvious impostors. A furnace that won’t light can also point to a tripped limit switch, a closed gas valve, or a dirty flame sensor — and replacing an ignitor won’t fix any of those. Watch what happens during a start cycle. If the igniter glows but no flame follows, the ignitor is doing its job and the problem is likely gas supply or the valve. If it never glows at all, that’s your strongest signal.
I’ve tested this myself with nothing more than a multimeter set to ohms. Pull the two wires off the ignitor terminals, touch a probe to each terminal, and read the resistance. Most functioning ignitors show somewhere between 40 and 90 ohms, though this varies by model. A reading of infinite resistance, or “OL” on most digital meters, means the internal element has broken and the part is dead. No continuity, no ignition, full stop.
It’s also worth a visual check with the power off and panel open. Cracks are sometimes visible to the naked eye, especially near the base where the ceramic meets the metal bracket. Not every failure shows visually, but when it does, it saves you the multimeter step entirely.
Turning Off Power and Gas Safely
This part isn’t optional, and I say that as someone who once skipped it because I was “only testing.” Locate your furnace’s dedicated electrical switch — it usually looks like a light switch mounted on or near the unit itself — and flip it off. Then go to your breaker panel and shut off the corresponding breaker too, since a mislabeled switch is more common than you’d think.
Shut off the gas supply at the shutoff valve on the line running into the furnace, turning the handle a quarter turn until it’s perpendicular to the pipe. You don’t strictly need the gas off to replace the ignitor itself, since you’re not touching the gas line, but it removes any risk while the burner compartment is open and you’re working with your hands close to the valve assembly.
Give the furnace a minute or two after shutting off power before you start working. Some models have a cooling fan that runs briefly after shutdown, and you don’t want to be mid-removal when it kicks on.
Removing the Access Panel and Locating the Ignitor
Most furnaces have a front or side access panel held on with a couple of screws or, on newer units, simple tabs that release with a firm push and slide. Behind that panel, the burner compartment houses the ignitor, flame sensor, and burners in a fairly compact space. The ignitor is usually mounted near the first burner, angled slightly so its tip sits directly in the gas stream. It looks different depending on brand — Carrier and Bryant units tend to use a bracket-mounted design that’s straightforward to access, while some Goodman and Trane models tuck the ignitor slightly further back behind the burner assembly. If you’re not sure which part you’re looking at, it’s the one with two wires running to it and a visible ceramic or silicon nitride tip, distinct from the flatter metal flame sensor rod nearby.
Most people miss this entirely, but taking a phone photo of the wiring and mounting position before you remove anything saves real time on reassembly. It sounds unnecessary until you’re holding a bracket forty minutes later trying to remember which way it was oriented.
Removing the Old Ignitor
Disconnect the two wire connectors from the ignitor terminals first. They typically pull straight off without much resistance — if one feels stuck, wiggle it gently rather than yanking, since the terminal itself can bend or snap under force.
Next, remove the one or two mounting screws holding the bracket in place. Keep a small dish or magnetic tray nearby for screws; furnace compartments have a way of swallowing dropped hardware into gaps you can’t easily reach. Once the screws are out, the ignitor and its bracket should lift free as a single unit on most models.
This is where the fragility really matters. The ceramic or silicon nitride element is genuinely delicate — it can survive years of thermal cycling in operation but snap instantly from a sideways knock during removal or installation. Handle it by the bracket or base, never by the tip, and set it down on a soft surface rather than bare metal.
Installing the Replacement
Confirm the replacement part matches your furnace’s make and model before installing — universal ignitors exist and work fine in many cases, but the mounting hole pattern and voltage (most residential units run 120 volt, though some use 24 volt control-side ignition) need to match your original. Cross-reference the part number stamped on the old bracket if you’re unsure.
From experience, the smarter move is to avoid touching the ceramic tip with bare fingers during installation. Skin oils can shorten the ignitor’s lifespan by creating uneven heating spots when the surface fires up. If you do touch it accidentally, a quick wipe with isopropyl alcohol before installing solves it.
Seat the new ignitor into the same bracket position you photographed earlier, secure the mounting screws, and reconnect the two wire connectors. They’re not polarity-sensitive on most designs, so there’s no wrong way to connect them, but push each connector on fully until it seats with a slight click or firm resistance.
Testing the Repair
Reinstall the access panel, restore gas supply if you shut it off, and flip the breaker and furnace switch back on. Set your thermostat a few degrees above room temperature to force a call for heat, then watch the burner compartment through the sight glass or viewing slot most panels include. You should see the ignitor glow within the first 30 to 45 seconds of the cycle starting, followed by ignition across the burners within a few seconds of that glow. If it lights cleanly and stays lit, you’re done. If it glows but nothing lights, double check your gas valve is fully open — it’s an easy thing to forget after working near it.
What surprised me was how often people replace the ignitor correctly and then panic when the furnace takes one extra cycle to fully catch. Give it two full on-off cycles before assuming something’s still wrong. Modern control boards run a full safety check sequence each time, and an ignitor that’s brand new sometimes needs a cycle to fully seat thermally.
What Most People Don’t Know
Ignitor failure rate isn’t random — it correlates heavily with how often your furnace short-cycles. Every time the system fires up and shuts down quickly, whether from a dirty filter, a bad thermostat setting, or an oversized furnace for the space, the ignitor takes a full thermal stress cycle. A furnace that short-cycles frequently can burn through ignitors in half the time of one that runs longer, steadier cycles. If you’ve replaced this part more than once in a few years, the ignitor usually isn’t the actual root problem — something upstream is forcing it to work harder than it should.
Checking your filter replacement schedule after an ignitor failure is worth the five minutes it takes. It’s the single most common hidden cause behind repeat failures, and it costs nothing to rule out.
A furnace ignitor is one of the few HVAC repairs that rewards patience over speed. Go slow around the ceramic tip, document the wiring before you disconnect anything, and give the system a full cycle or two before declaring victory. If you’ve replaced it twice in under three years, take a look at what’s forcing those short cycles — that’s the fix that actually sticks.
