4 flashes
Open limit or rollout
This code typically points to
- Airflow restriction (dirty filter/coil)
- Blower issue
- Overfiring
- Open limit or rollout circuit
- Blocked vent causing rollout
Next checks to confirm
- Verify airflow, static pressure, and blower operation
- Verify firing rate and input match nameplate
- Inspect limit and rollout circuit continuity; determine which safety opened
Escalation
Rollout trip is a hard combustion safety problem — do not reset without finding root cause.
Reset behavior
Self-reset limit clears when temperature falls; manual-reset rollout requires physical reset after root cause correction.
Safety Critical
Immediate concern