Furnace attempts to start but shuts down quickly; LED status light flashes twice repeatedly.

Safety first: Turn off power to the furnace before opening any panels. Do not blow into pressure switch tubing with the furnace powered.

Step-by-step checks:

• 1. Inspect pressure switch tubing: Locate the round pressure switch near the inducer assembly. Remove the small rubber or silicone tube(s) and check for water, debris, or cracks. Blow through the tube away from the furnace to clear any blockage. Reattach firmly.
• 2. Check condensate drain (if high-efficiency Philco model): Ensure the condensate trap and drain lines are not clogged or frozen. A backed-up condensate line can hold the pressure switch closed. Clean the trap and flush the line with warm water if needed.
• 3. Inspect vent and intake pipes: For PVC vented Philco furnaces, go outside and verify the exhaust and intake terminations are clear of leaves, snow, nests, or screens. Remove any obstructions.
• 4. Test pressure switch operation (basic): With power off, gently tap the pressure switch housing with a screwdriver handle to free a stuck diaphragm. Restore power and call for heat. If the code persists, the switch may be stuck closed internally.
• 5. Check inducer operation: Confirm the inducer motor starts only when there is a call for heat. If it runs constantly or not at all, the control board may be mis-driving it, causing incorrect pressure at the switch.

When to call a professional: If the pressure switch remains stuck closed after tubing and vent checks, have a technician test the switch with a manometer and replace it with a Philco-rated pressure switch if out of spec.