3+1
Limit switch open
This code typically points to
- Airflow restriction
- Overfiring / temperature rise problem
- Blower issue
Next checks to confirm
- Check filter and duct restriction
- Verify blower operation
- Verify temperature rise and input rate
Escalation
Burner off; blower operation continues per sequence
Reset behavior
Auto clears after switch recloses.
Safety Critical
Immediate concern