The status LED on the Lennox furnace control board flashes 1 time repeatedly; the furnace will not start the heating cycle.

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

Possible Causes

No gas supply to the Lennox furnace, Faulty hot surface ignitor, Misaligned or dirty flame sensor, Faulty gas valve or control board ignition circuit

Safety: Turn off power and gas before servicing. If you smell gas, evacuate and call the gas utility.

1. Confirm thermostat call: Ensure the thermostat is set to HEAT and the temperature is above room temperature.
2. Check gas shutoff: Verify the manual gas valve to the furnace is open.
3. Inspect ignitor and flame sensor: Access the burner compartment, visually inspect the ignitor for cracks, and clean the flame sensor as described earlier.
4. Reset furnace: Restore power and gas, then cycle power to clear the lockout and observe the ignition sequence.

If the LED 1-flash code returns, professional gas and ignition diagnostics are required.

Hard 4/5

Hot Surface Ignitor

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