3 flashes
Pressure switch stuck open
This code typically points to
- Not explicitly detailed in accessible legacy brochure snippet
Next checks to confirm
- Verify inducer operation
- Inspect pressure-switch hose, vent/intake blockage, drain issues on condensing units if applicable, and pressure-switch wiring
Escalation
Furnace heat cycle inhibited until pressure-switch proving is restored
Reset behavior
Clears when the pressure-switch circuit closes properly during heat call.
Urgent
Fix now