4 blinks
Pressure switch circuit closed / pressure switch stuck closed
This code typically points to
- Pressure-switch contacts remain closed during off cycle
- Welded or stuck contacts
- Improper reopening from previous heat call
Next checks to confirm
- Verify switch opens in off cycle
- Inspect contacts/wiring
- Inspect hoses for moisture
- Confirm switch operation across a full call cycle
Escalation
Furnace will not begin ignition sequence if pressure switch fails to reopen from previous call
Reset behavior
Clears once pressure switch reopens correctly and fault is removed.
Urgent
Fix now