Lennox
Humidifier Control Failure
Thermostat fails to control whole-home humidifier connected to Lennox furnace/air handler.
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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
Incorrect humidifier wiring to Lennox control board HUM terminals, Misconfigured humidifier type in thermostat setup, Failed humidifier relay on Lennox board, Open or shorted humidifier control wires
How to Fix / Troubleshooting
Safety warning: Turn off power to the furnace/air handler before working on humidifier wiring.
- 1. Verify thermostat configuration:
- Ensure humidifier is enabled and correct type (bypass, powered, steam) is selected.
- 2. Inspect HUM wiring:
- Check connections from Lennox board HUM terminals to the humidifier solenoid or control.
- Tighten any loose wires.
- 3. Test humidifier manually:
- With power on, command humidity from thermostat and listen for humidifier operation.
- A technician can jumper HUM to test the humidifier independently.
- 4. Replace board or humidifier control if relay is failed:
- If the board does not send power when commanded, the HUM relay or board may need replacement.
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Repair Difficulty
Medium
3/5
Required Part
Lennox Furnace/Air Handler Control Board
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