Why does my furnace igniter keep burning out?

If your furnace igniter keeps burning out, the igniter is rarely the real problem. The part is a consumable: a small ceramic element that goes from room temperature to well over 1,000 °C in seconds, every time the furnace lights. A healthy one survives 3 to 7 years of that. One that dies each winter is being damaged by something else in the furnace or the house, and that is the thing to find.

Silicon carbide versus silicon nitride: which igniter you have

Older furnaces use silicon carbide igniters: a grey, speckled, flat or spiral element brittle enough to crack if a screwdriver bumps it. Most newer furnaces use silicon nitride: a smooth, darker rod or blade that heats faster, draws less current and tolerates vibration. Both types typically last 3 to 7 years, with nitride toward the long end and carbide toward the short end in a furnace that cycles often.

The two are not interchangeable by eye. Igniters come in 120-volt, 80-volt and 24-volt versions, and the control board is matched to one of them. A part that fits the bracket but not the board's voltage glows too hot and dies young, or glows too cool and never lights the gas, which is the fault described in why an igniter glows but the burners will not light.

Why a new igniter fails again within a year or two

• Skin oil from handling. Fingerprints on a carbide element bake into hot spots that crack it weeks or months later. The part is held only by its ceramic base, and one that has been touched should not be installed.
• High line voltage. A 120-volt carbide igniter is built around nominal voltage. A house that sits several volts high, which happens close to the street transformer, runs the element hotter on every cycle, so a technician should measure voltage at the furnace with the igniter energized.
• Short-cycling. A furnace that lights 10 or 12 times an hour instead of 3 to 5 puts three winters of ignition cycles on the part in one. A clogged filter, an oversized furnace and a thermostat set to cycle too tightly are the usual reasons, and our guide to furnace short-cycling covers each.
• Condensate dripping on the element. On a high-efficiency furnace, a leaking collector box gasket or a blocked drain lets acidic water into the burner compartment. Water on a glowing ceramic cracks it, and rust streaks under the burners give it away.
• The wrong universal part, or the right part in the wrong place. An igniter that sits too deep in the flame is cooked by the burner after it has done its job. One that sits too far back lets gas build up and light with a thump.
• A control board that holds the igniter on too long. A sticking relay keeps the element glowing through the whole burn instead of switching it off once flame is proven.
• Dirty burners and delayed ignition. Each small boom at light-off is a shock load on a brittle part.

What you can check yourself, and what to leave alone

You can narrow this down without touching the igniter. Do not pull it out to look at it: carbide elements break from handling, and the burner compartment is gas work for a TSSA-licensed technician.

• Find the old invoices. Count how many igniters the furnace has had and how far apart. Less than two years between failures means a root cause, not bad luck.
• Time the cycles. If the burners run for less than five minutes and relight a few minutes later, the furnace is short-cycling.
• Check the filter and open every supply register. Restricted airflow trips the limit switch and forces extra ignition cycles.
• Shine a flashlight through the burner sight glass or door louvres and look for rust trails or water droplets below the burners.
• Listen at start-up. A soft whoosh is normal. A bang or a rumble before the flame settles is delayed ignition.
• Keep the box of the failed part if the technician leaves it. A universal part number on a furnace that keeps eating igniters is worth mentioning on the next call.

When a failing igniter is a call-today problem

A dead igniter is not dangerous in itself. The furnace tries to light, proves no flame and locks out with the gas valve closed. The urgency comes from the weather and from the symptoms around the failure.

• Call now if the house has no heat and the forecast is below freezing. Pipes in exterior walls are at risk once the house cools right down.
• Call now if ignition comes with a bang, a puff of flame at the burner door or a gas smell.
• Call now if you can see water inside the burner compartment or on the control board.
• It can wait a day or two if the furnace still lights on the second or third try and the house holds temperature. Book it anyway, because each failed attempt adds wear and the lockout will come.

Fixing the cause, and what an igniter replacement costs

Replacing a hot surface igniter costs $200–$450 installed, and the $90–$150 diagnostic visit is folded into the repair if you go ahead. On a repeat failure, that visit should cover more than the swap: a voltage reading, a resistance reading on the new part, igniter position against the burner, the drain and collector box, and a count of cycles per hour. If the last invoice only says igniter replaced, ask what else was checked.

Where an original carbide igniter keeps failing, a silicon nitride upgrade kit is often the lasting fix. These kits include brackets and a wiring adapter so a tougher nitride element can take the carbide one's place, provided the kit matches the furnace's igniter voltage and the element lands in the same spot in the flame. It is the better choice in a furnace that vibrates or cycles hard, and we price it in writing before fitting it.

ZK Mechanical's TSSA-licensed technicians look for why the last igniter failed before fitting the next one. The price detail is in what a furnace igniter costs, and other ignition faults are grouped under heating answers. To book furnace repair, call (647) 801-1252 or send a request online.

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