31.1
Open main pressure switch / pressure switch did not function properly
This code typically points to
- Low/main pressure switch not proving
- Vent/condensate/tubing issue
- Switch calibration issue
- Sagged vent, plugged trap, water in tubing, marginal inducer, wind effects
Next checks to confirm
- Verify inducer operation and actual proving path
- Inspect condensate drain, tubing, and venting
- Verify switch function
Escalation
If HSI glows with inducer disconnected, manual says shut furnace down immediately.
Reset behavior
Clears when proper proving returns.
Urgent
Fix now