Lennox
No Power to Thermostat
Thermostat is completely blank with no display and no response to touch or buttons.
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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.
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Possible Causes
Tripped furnace/air handler breaker, Blown low-voltage fuse on Lennox control board, Open R or C wire between thermostat and indoor unit, Failed 24V transformer in Lennox indoor unit
How to Fix / Troubleshooting
Safety warning: Turn off power at the breaker before removing furnace panels or touching wiring.
- 1. Check breakers and switches:
- Ensure the indoor unit breaker and service switch are ON.
- 2. Inspect control board fuse:
- Remove the blower door and locate the low-voltage fuse on the Lennox board.
- Replace if blown with the same amperage.
- 3. Verify thermostat wiring:
- Confirm R and C wires are firmly connected at both thermostat and control board.
- 4. If still blank:
- Have a technician test the 24V transformer and replace if no voltage is present.
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Repair Difficulty
Medium
3/5
Required Part
24V Transformer in Lennox Indoor Unit
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