Why won't my furnace igniter glow?
Updated August 2026
A furnace igniter that stays dark when the burners should light is almost always a cracked hot-surface igniter, the brittle silicon-carbide or silicon-nitride rod that ages out after 3 to 5 heating seasons. These elements are fragile by design, and years of on-off cycling plus one careless fingertip during a past repair are enough to fracture the rod so it no longer glows. Confirm the furnace is actually calling for heat first, then work down the list below, which runs from the cheap and likely to the rare and expensive.
Safety first: a hot-surface igniter runs on 120 volts while it glows, so cut power at the furnace switch or breaker before you touch it, and hold a replacement by the white ceramic base only, since skin oil or a light tap cracks the rod. Never keep cycling a furnace that fails to light: most control boards lock out after 3 tries because unburned gas can pool, and a working carbon-monoxide detector belongs on every level before you troubleshoot a gas appliance.
Causes, most likely first
| Cause | How likely | The fix | Typical cost |
|---|---|---|---|
| Cracked hot-surface igniter | Most common | Replace the silicon-carbide or silicon-nitride igniter with the exact matching part; handle it only by the ceramic base, never the rod. | $15–50 part, $150–350 installed |
| No call for heat reaching the board | Common | Set the thermostat to heat above room temperature, fit fresh batteries, and press the blower-door safety switch fully closed. | Free |
| Blown low-voltage control-board fuse | Occasional | Swap the 3-amp automotive blade fuse on the board, then trace the shorted wire that popped it. | $5 fuse |
| Failed control board or igniter relay | Occasional | The board is not sending line voltage to the igniter; a tech meters the terminals and replaces the board. | $300–600 |
| Broken igniter lead or loose plug | Rare | A cracked igniter wire or unseated connector kills the glow; reseat or repair the plug. | $0–150 |
Check these first
- Set the thermostat to heat several degrees above the room, then watch through the sight glass: a healthy igniter glows bright orange within 30 to 45 seconds of the call.
- Confirm the blower-compartment panel is seated all the way so the door safety switch closes, since a panel left ajar keeps the igniter dark.
- Cut power at the furnace switch for 30 seconds to clear a lockout, because many boards stop trying after 3 failed attempts.
- With the power off, inspect the rod for a hairline crack, a chip, or a chalky white spot, any of which means it is finished even if it looks whole.
- Check the control board for a blown 3-amp blade fuse and reseat the igniter plug.
Prevent it next time
The igniter is a wear part, not a lifetime one, so treat it like a filter and stay ahead of the failure. Most last 3 to 7 heating seasons, and swapping it on the recommended replacement schedule, plus keeping a spare in the furnace closet, turns a no-heat night into a five-minute part change. See what the igniter actually does, how that stacks up against a normal service life, and a walkthrough in replacing a furnace igniter.
When to call a pro
Call a technician when a brand-new igniter still will not glow, when the board shows no line voltage at the igniter terminals, or when you smell gas at any point. A diagnostic runs $100–200, an igniter swap $150–350, and a control-board replacement $300–600. Handling 120-volt terminals and gas-valve timing is not the place to guess, and bolting a good part onto a dead board just wastes money.
Most of the causes above are maintenance problems wearing a disguise. OnOtto keeps the boring prevention on schedule so the 2 a.m. version doesn't happen.
Stop chasing symptoms, free for 30 daysFrequently asked questions
Can I clean a furnace igniter instead of replacing it?
No. A hot-surface igniter is not a flame sensor: you revive a flame sensor by scuffing off oxidation, but an igniter is brittle silicon carbide or silicon nitride that cracks the moment you rub or wipe it. If it glows weakly or not at all, replace the whole rod, a $15 to $50 part. The only cleaning that helps is gently vacuuming dust from around the burner assembly with the power off, and even that will not bring a cracked igniter back.
How can I tell if it is the igniter or the flame sensor?
Watch the sequence. If the igniter never glows orange, the fault is upstream at the igniter, board, or power. If it glows, the burners light, then the flame drops out after 3 to 7 seconds, that is a dirty flame sensor, a separate part. Igniter faults mean no flame at all; flame-sensor faults mean a flame that lights and quits. Timing the failure to the second tells you which of the two to chase first, and saves buying the wrong part.
Why did my furnace igniter fail so soon?
Igniters are fragile, and a few things cut into their 3-to-7-season life. Constant on-off cycling from a dirty filter fires the igniter thousands of extra times a winter. A power surge or high line voltage overstresses the element. And touching the rod during a past repair leaves skin oil that bakes into a weak spot and later a crack. Changing the filter on schedule and handling the part only by its base are the two habits that buy the most seasons.
Is it safe to run the furnace after I replace the igniter myself?
Yes, if you killed power before the swap, seated the new igniter without touching the rod, closed the blower door, and the burners now light cleanly and stay lit. Watch the first two or three cycles: the flame should be steady blue and the unit should shut off normally. Keep a carbon-monoxide detector nearby, and if the burners boom on ignition, throw soot, or burn a lazy yellow flame, shut it down and call a pro.