Furnace will not ignite; inducer may run briefly or not at all; LED flashes code 31 (pressure switch open or failed to close).

Safety: Turn off power and gas before servicing. Do not operate the furnace with venting disconnected.

Steps:

• Inspect vent and intake: Go outside and check the PVC vent and intake terminations for leaves, snow, ice, bird nests, or debris. Clear any obstructions. Ensure vent terminations meet Keeprite installation clearances.
• Check condensate system (condensing models): Locate the condensate trap and drain tubing. Remove and flush the trap with warm water to clear sludge. Ensure the drain line slopes continuously to the drain and is not kinked.
• Inspect pressure switch tubing: With power off, remove the rubber hose from the pressure switch and inducer port. Check for water, cracks, or blockages. Blow through the hose to clear it and reinstall securely.
• Test pressure switch operation: Restore power and call for heat. Listen for the click of the pressure switch closing shortly after the inducer starts. If it does not close and venting is clear, the switch may be defective.

Important: Never bypass or jumper the pressure switch for normal operation. If the switch will not close with proper venting and inducer operation, have it tested and replaced by a technician.