What a hot surface igniter does
The igniter is a small element, usually silicon carbide or silicon nitride, that heats to well over a thousand degrees when energized. Once it reaches temperature, the control board opens the gas valve and the burner ignites from the glowing element. Seconds later the flame sensor confirms combustion and the igniter powers down.
Eliminating the standing pilot saved a meaningful amount of gas over a heating season, but it introduced a consumable part. Igniters are expected to be replaced periodically over a furnace's life.
Why igniters fail
- Thermal fatigue — heating and cooling thousands of times eventually cracks the element
- Hairline cracks that are invisible without close inspection but break the circuit
- Contamination from oils or dust baked onto the surface
- Voltage irregularities shortening element life
- Physical damage during unrelated service work
- Frequent cycling, which is why short cycling shortens igniter life
Symptoms of a failed igniter
With a failed igniter the furnace goes through its normal pre-purge, the inducer runs, and then nothing happens — no flame, no heat, and after a few attempts a lockout code. There is often no clicking, because most hot surface systems have no spark. Homeowners generally describe it as a furnace that runs but produces no heat, or one that will not start at all.
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Replacement and verification
Igniters are widely stocked and generally inexpensive relative to other furnace parts, and replacement is usually a same-visit repair. Good practice goes further than swapping the element: a technician should inspect the burner assembly for the conditions that stressed the igniter, verify gas pressure, confirm draft, and check that the furnace is not cycling more often than it should.
Handling matters too. Skin oils on a silicon carbide element can create a hot spot, so igniters are handled by the ceramic base rather than the element.
Related reading
If your furnace is failing to light, start with furnace ignition problems for the full sequence of operations, then compare against furnace won't turn on if the unit is completely unresponsive.
Furnace Safety Comes First
If you smell gas, see smoke or fire, or suspect carbon monoxide, stop troubleshooting. Move everyone out of the affected area, then contact your gas utility or emergency services from a safe location.
Never bypass a pressure switch, limit switch, rollout switch, door switch or flame sensor, and never attempt gas valve, burner, heat exchanger or live-voltage work. Those controls exist to shut the furnace down before a dangerous condition develops.
Read our carbon monoxide safety guide