What This Error Means

The furnace control detected the pressure-switch circuit closed when it should have been open, usually before the inducer established draft.

Symptoms You May Notice

Furnace will not begin ignition; inducer may not proceed through the normal sequence; fault appears immediately after a call for heat; no burner operation.

Common Causes

Pressure switch contacts stuck closed; tubing exposed to unintended vacuum; water or debris affecting the switch; shorted wiring; incorrect wiring; control-board input fault.

Safe Troubleshooting Steps

1. Turn off power. 2. Inspect pressure-switch wiring for crossed or pinched conductors. 3. Inspect tubing for incorrect routing, water or an unintended vacuum source. 4. With the furnace off and no draft present, a technician should verify that the switch contacts are open. 5. Confirm the switch opens and closes at the specified pressure. 6. Test the control input if the switch and wiring are correct.

Parts Commonly Involved

Pressure switch; pressure tubing; wiring harness; inducer assembly; integrated furnace control.

When to Call a Technician

Yes, because safe diagnosis requires switch and draft testing.

Safety Notice

Never bypass or permanently jumper a pressure switch. Replace it only with the specified part and correct the underlying cause.

Manufacturer Documentation