Component
Hot-surface ignitor
The hot-surface ignitor is the ceramic element that glows to ignite the gas on modern furnaces. It heats during every cycle and is a wear item: failures show as no ignition, ignition lockouts, or a furnace that only lights sometimes.
Short answer
An ignitor failure usually appears as an ignition code after the control's trials fail. You can watch the ignitor glow through the burner access window if your furnace has one, but testing it is a technician's job: the element's resistance and its glow pattern tell whether it is failing. Repeated resetting after ignition failures is exactly what manufacturers warn against.
How it works
When the pressure switch proves draft, the control energizes the ignitor for a set period (Carrier's sequence, for example, runs the ignitor for about 15 seconds), then opens the gas valve. The ignitor must reach temperature within the trial window or ignition fails.
Why they fail
Silicon-nitride and silicon-carbide ignitors are brittle: cracks from handling, thermal stress over thousands of cycles, and electrical failure of the element all end their life. A furnace that lights only on the second or third try often has an ignitor that is marginal.
Diagnosis
A technician measures the ignitor's resistance against specification, watches its glow through the cycle, checks the voltage reaching it, and confirms the gas valve opens only after the ignitor is hot. Replacing an ignitor is straightforward; finding why it failed early is the real diagnostic work.
Related
Questions people ask
How long do hot-surface ignitors last?
They are a wear item with no guaranteed life; many last a decade or more, while others fail earlier depending on cycles and voltage quality. They are inexpensive relative to the service call.
Can I clean an ignitor?
No. Cleaning or touching the element can damage it. If it is contaminated or cracked, it is replaced.
Why does my furnace sometimes take two tries to light?
A marginal ignitor, low gas pressure at light-off, or a weak flame signal can all cause first-try failures. The control's fault history shows how often and when.
Need this looked at?
Call BC Wide with the brand, model number and anything on the display. Or
Request service online with this page attached.