Dirty flame sensors trigger shutdowns after the burner lights
Why it happens here
Long heating cycles and normal combustion residue can coat a flame sensor. The burner may light briefly, but the control does not confirm a stable flame and shuts the furnace down. Repeated starts are especially noticeable in winter when the system is working harder.
Our approach
We inspect the sensor, burner flame, wiring, and control response before deciding whether cleaning or replacement is needed. Then we run multiple heating calls and confirm the burner remains stable. We also look for an underlying combustion or airflow issue that could cause the fault to return.