Furnace does not light or goes into lockout

What is going on

Use the 2-stage IFC troubleshooting chart when the furnace will not ignite or keeps locking out.

Likely causes

• Heat call not reaching the control or a wiring problem
• Dip switch settings incorrect
• Inducer fault
• Flame sense problem
• Gas valve or ignition problem
• Airflow restriction or limit problem
• Overfire condition

Check in this order

1. Disconnect power before servicing and use a qualified technician.
2. Confirm a steady H on the display. If flashing, check dip switches.
3. Check thermostat wiring and 24 VAC on W1 and W2 at the control.
4. Confirm the inducer starts on low speed and runs the 30-second pre-purge.
5. Check the inducer and its wiring if it does not run or faults 45, 46 or 57 appear.
6. Confirm spark electrodes spark and gas valve stays energized during the ignition trial.
7. If there is no flame, check codes 11 or 13 and the flame sense circuit.
8. Check airflow for dirty filters, blower wheel, dampers or closed registers.
9. Check limits and rollouts. Reset rollouts only after finding the cause.
10. Check that the furnace is not overfiring by checking the temperature rise and gas valve, orifice and gas pressure.
11. If lockout occurs, shut off main power, wait 30 seconds and restore power, or remove the heat call and re-establish it.
12. If the problem persists after these checks, repeat the sequence until trouble-free operation.

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