What This Error Means

A four-blink code means the pressure switch remains closed when the furnace control expects it to be open. The control sees an abnormal pressure-switch signal before or outside the proper inducer sequence.

Symptoms You May Notice

Furnace may not begin the ignition sequence; code may appear before the inducer starts; no burner operation; fault may return immediately after a reset.

Common Causes

Pressure-switch contacts stuck closed; shorted or crossed wiring; water or debris in the switch or tubing; incorrect tubing connection; unintended draft; blocked pressure port; integrated furnace-control input fault.

Safe Troubleshooting Steps

1. Turn off furnace power. 2. Inspect pressure-switch wiring for pinched, crossed, or damaged conductors. 3. Inspect tubing for water, debris, kinks, damage, and correct routing. 4. Do not disconnect or jumper safety controls while the furnace is powered. 5. A qualified technician should verify the switch is open with no inducer draft, test continuity, inspect the pressure ports, and evaluate the furnace control if the switch and wiring are normal.

Parts Commonly Involved

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

When to Call a Technician

Yes. Correct diagnosis requires pressure-switch and electrical testing.

Safety Notice

Never bypass a pressure switch. Turn off power before inspecting wiring or tubing near the inducer and control compartment.

Manufacturer Documentation