How hot surface ignition works
On a call for heat, after the inducer establishes draft and the pressure switch closes, current flows through a small silicon carbide or silicon nitride element. It glows bright orange, reaching well over 1,800°F in roughly 15 to 45 seconds. The gas valve then opens and the burners light off the glowing element. The ignitor de-energizes once flame is proven.
Symptoms of a failing ignitor
- The inducer motor runs, then the furnace goes silent without burners lighting.
- The furnace attempts ignition three times, then locks out.
- No orange glow is visible through the furnace sight glass during the attempt.
- The furnace works intermittently — it lights on some attempts and not others.
- The furnace suddenly fails during the first serious cold snap of the season.
Why ignitors crack
| Factor | Effect |
|---|---|
| Thermal cycling | Repeated heating and cooling embrittles the ceramic element — the dominant wear factor |
| Cycle count | Ignitors are rated in cycles; a long Buffalo heating season burns through them faster |
| Physical handling | Oils from fingers and small bumps create weak points that later crack |
| Voltage irregularities | Consistently high line voltage shortens element life |
| Short cycling | More cycles per day means proportionally faster wear |
What replacement involves
- 1
Verify it is actually the ignitor
Resistance is measured across the element and the sequence is observed. A furnace that fails on the pressure switch never gets to ignition at all, and replacing the ignitor would not help.
- 2
Match the correct part
Ignitors vary by element type, mounting bracket, and connector. The wrong part physically fits sometimes and still fails early.
- 3
Install without touching the element
Handled by the ceramic base only, positioned exactly in the burner flame path per specification.
- 4
Verify full operation
Complete heat cycles are observed, flame sensor signal read, and temperature rise confirmed before the job is finished.
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Not a DIY repair
The ignitor sits inside the combustion compartment alongside the gas manifold and burners. Improper positioning causes delayed ignition, which can produce a small explosion inside the heat exchanger. This is work that belongs to someone with gas training.