Inducer runs, ignitor glows, burners light briefly then shut off; LED shows 3 flashes on York board.

Safety: Turn off power before disconnecting any wires. Do not bypass safety switches for operation.

• Visual inspection: Remove the burner door. Locate the pressure switch and its two low-voltage wires. Inspect for rubbed-through insulation or wires touching ground or each other.
• Check tubing and vent: Ensure the pressure tubing is properly connected and not pinched. Confirm vent and intake are clear as with a 2-flash fault.
• Test switch at rest: With power off and inducer not running, disconnect one wire from the pressure switch and use a multimeter on continuity. The switch should be open with no call for heat. If it reads closed, the switch is stuck and should be replaced with the correct York-rated switch.
• Board reset: Restore power and reset the furnace by cycling power off for 30 seconds. If the 3-flash returns immediately with no call for heat, suspect a shorted switch or control board fault.
• Call a technician: If wiring and switch test good, the integrated furnace control (IFC) board may be defective and should be diagnosed and replaced by a professional.