The status LED on the Lennox furnace control board flashes 4 times; the furnace may ignite then shut off after a few seconds.

Safety Warning

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

Dirty or restrictive Lennox air filter, Blocked supply or return ducts, Failed indoor blower motor or capacitor, Faulty high limit switch or rollout switch

How to Fix / Troubleshooting

Safety: Turn off power and allow the furnace to cool before inspection.

1. Replace filter: Install a clean, properly sized Lennox-approved filter.
2. Check registers and ducts: Open all registers and ensure returns are not blocked.
3. Inspect blower: Verify the blower starts and runs smoothly. If it does not start, the motor or capacitor may be bad.
4. Manually reset rollout (if present): Some rollout switches have a manual reset button. If tripped, press to reset once. If it trips again, shut the system down and call a technician.

Repair Difficulty

Medium 3/5

Required Part

High Limit Switch

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