43
Low-heat pressure switch open while high-heat pressure switch is closed
This code typically points to
- Sag in vent pipe
- Clogged trap/drain line
- Improperly plumbed drain tubing
- Switch circuit issue
Next checks to confirm
- Check vent sag, condensate trap/line, tubing, pressure switch circuit, draft timing
Escalation
If vent/drain path is right and switch circuit checks out, board or pressure-sensing integrity issue is next.
Reset behavior
Fault logic tied to pressure-switch state relationship.
Urgent
Fix now