13 red flashes
Second-stage/high pressure switch open with call for second-stage heating
This code typically points to
- Faulty inducer
- Blocked vent
- Broken or disconnected hoses
- Disconnected pressure-switch or inducer wiring
- Faulty pressure switch
Next checks to confirm
- Verify second-stage inducer/draft path
- Inspect tubing and wiring
- Use manometer to verify vent pressure
Escalation
Follows active fault logic; clears when proof is correct.
Reset behavior
Clears when proof established.
Urgent
Fix now