Lennox furnace control board LED is completely off; furnace is non-responsive.

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

Tripped furnace breaker, Blown internal fuse on Lennox control board, Failed 120V-24V transformer, Loose door switch not engaged

Safety: Turn off breaker before removing panels.

1. Check breaker and switch: Ensure the furnace breaker and service switch are ON.
2. Verify door switch: Confirm the blower door is properly installed and depressing the door safety switch.
3. Inspect board fuse: Check the low-voltage blade fuse on the control board and replace if blown. If it blows again, there is a short.
4. Transformer check: A technician should test for 120V into and 24V out of the transformer.

Medium 3/5

24V Transformer

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