The igniter on a gas dryer is a small silicon carbide component that glows orange-hot to ignite the gas burner at the start of each heat cycle. When it fails, you can often hear the gas valve open with a faint click but the burner never lights — the drum keeps spinning through a cold cycle.
Igniter failure is the most common cause of a gas dryer not heating. You can sometimes observe the igniter through the burner access panel — if it glows bright orange and then the burner doesn't light, the radiant sensor or gas valve coils may be the issue. If it doesn't glow at all, the igniter itself has failed.
Igniter replacement is a straightforward repair: the component is inexpensive, typically available on the service vehicle, and replacement takes 30–45 minutes on most models.