Status LED on Lennox furnace control board flashes 3 times; furnace may start then shut down quickly.

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

Pressure switch contacts welded closed, Shorted pressure switch wiring, Inducer motor running continuously, Faulty Lennox control board sensing circuit

How to Fix / Troubleshooting

Safety: Turn off power before testing the pressure switch.

1. Inspect wiring: Ensure pressure switch wires are not shorted together or pinched.
2. Tap pressure switch: Lightly tap the pressure switch housing; if contacts are stuck, this may temporarily free them, indicating the switch should be replaced.
3. Check inducer operation: Confirm the inducer is not running constantly with no call for heat, which may indicate a control board issue.

A stuck-closed pressure switch usually requires replacement by a technician.

Repair Difficulty

Hard 4/5

Required Part

Pressure Switch

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