What This Error Means

The furnace control expected the pressure switch to close after the inducer started, but the switch remained open. Ignition is prevented because adequate combustion-air movement or vent draft has not been proven.

Symptoms You May Notice

No heat; inducer runs but burners do not light; repeated startup attempts; pressure-switch fault displayed; possible water in tubing or condensate system.

Common Causes

Blocked intake or exhaust vent; restricted flue; condensate trap or drain blockage; water in pressure tubing; cracked, loose or kinked tubing; weak or failed inducer; faulty pressure switch; blocked pressure port; wiring fault.

Safe Troubleshooting Steps

1. Turn off power. 2. Check outdoor intake and exhaust openings for snow, ice, nests or debris. 3. Inspect condensate drains and trap for blockage or improper routing. 4. Inspect pressure tubing for water, cracks, kinks and secure connections. 5. Inspect the pressure port for obstruction without enlarging it. 6. Confirm the inducer starts and runs smoothly. 7. A qualified technician should measure draft pressure and verify switch operation against the furnace specifications.

Parts Commonly Involved

Pressure switch; pressure tubing; inducer motor and wheel; intake and exhaust venting; condensate trap and drain; integrated furnace control; wiring.

When to Call a Technician

Yes, particularly when venting, inducer performance or draft-pressure measurement is involved.

Safety Notice

Never jumper or bypass a pressure switch. It verifies that combustion gases can be vented safely.

Manufacturer Documentation