Furnace attempts to start but shuts down quickly; LED on Tappan control board flashes 2 times repeatedly.

Safety: Turn off power to the furnace before touching wiring or tubing.

Steps:

• Locate the pressure switch on the inducer housing. Disconnect the rubber tubing and inspect for water, debris, or kinks. Blow gently through the tubing to clear any blockage and reinstall firmly on both the pressure switch and inducer port.
• With power off, disconnect one wire from the pressure switch and check continuity across the switch with a multimeter. With no inducer running, the switch should be open. If it reads closed, the switch is stuck and should be replaced.
• Inspect the inducer motor wiring. If the inducer runs continuously even with no call for heat, the control board relay may be stuck closed.
• Verify that the pressure switch wires are on the correct terminals as per the Tappan wiring diagram on the furnace door.

Note: Never bypass the pressure switch for operation; it is a critical safety device.