Furnace will not start; LED on control board flashes 1 time repeatedly; inducer motor does not start.

Safety first: Turn off power to the furnace at the service switch and shut off gas at the gas cock before removing panels. Allow the furnace to cool.

Steps:

• Remove the blower/ burner compartment door to access the Tappan control board and LED.
• Verify the thermostat is calling for heat (set to HEAT and temperature above room temp). Check 24 VAC between R and C at the control board. If no voltage, inspect thermostat wiring and transformer.
• Check all manual reset rollout switches and high limit switches in series with the control. On many Tappan furnaces these are mounted around the burner box and heat exchanger. Press the red reset button if present. If a rollout is tripped, investigate for blocked flue or burner issues before resetting.
• Inspect wiring harnesses to the limit string for loose or burned connectors. Reseat any loose spade terminals.
• If all safeties are closed (continuity present) and 24 VAC is present at R and C but the board still shows 1 flash and will not start the inducer, the integrated furnace control may be defective and should be tested or replaced.

When to stop: If a rollout switch is tripped and you see signs of overheating, melted wiring, or a warped burner box, do not reset repeatedly—contact a qualified HVAC technician.