4 flashes
Open high limit
This code typically points to
- Not explicitly detailed in accessible legacy brochure snippet
Next checks to confirm
- Check airflow restriction
- Filter condition
- Blower operation/speed
- Duct restriction
- Limit circuit
Escalation
Burner shutoff / heating interruption until limit closes or fault is corrected
Reset behavior
Clears after limit circuit returns to normal and control allows operation.
Safety Critical
Immediate concern