Status LED flashes twice repeatedly, furnace starts but shuts down shortly after ignition

Safety first: Turn off power to the furnace at the breaker or service switch before working inside the cabinet.

Steps to check:

• Inspect pressure switch tubing: Remove the front panel. Locate the round pressure switch and its rubber tubing to the inducer housing. Pull the tubing off and check for water, debris, or cracks. Blow gently through the tube to clear any blockage. Replace if brittle or cracked.
• Check venting and inducer: Make sure the PVC exhaust and intake pipes (if 90%+ model) are not blocked by leaves, snow, or nests. Verify the inducer motor wheel spins freely and is not obstructed.
• Test the pressure switch (for qualified persons): With power off, disconnect the wires and check continuity across the switch with a multimeter. It should be open with no call for heat. If it reads closed all the time, the switch is stuck and should be replaced with a Gibson-approved part.
• Reset and test: Reconnect tubing and wires, restore power, and call for heat. If the code returns, the pressure switch or control board may need professional diagnosis.