Status LED flashes three times, inducer runs but burners do not light

Safety first: Shut off power and gas before removing vent connections. Working on venting at height or on roofs should be done by a professional.

Steps to check:

• Inspect vent terminations: Go outside and check the furnace exhaust and intake (if applicable). Remove any visible obstructions such as leaves, ice, or nests. Ensure vent screens are clear.
• Check condensate drain (for condensing Gibson furnaces): A clogged condensate trap or hose can flood the inducer housing and prevent proper pressure. Clean the trap and hoses, and ensure they slope correctly to the drain.
• Examine pressure tubing: Inside the furnace, remove and inspect the rubber tubing from the inducer to the pressure switch. Clear any moisture or debris and reseat firmly on both ports.
• Test inducer operation: Restore power and call for heat. Confirm the inducer starts promptly and runs smoothly. If it hums, is noisy, or fails to start, the inducer motor may be failing.
• If the switch never closes: The pressure switch may be out of calibration or defective. Replacement with the correct Gibson-rated pressure switch is recommended by a technician.