Trane
Humidifier Control Failure
Thermostat does not control whole-home humidifier even when humidity is low
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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
Humidifier not enabled in thermostat configuration, Miswired HUM or accessory terminals, Failed humidifier solenoid or control board, Incorrect humidity setpoint or outdoor lockout settings
How to Fix / Troubleshooting
Safety warning: Turn off power to the furnace/air handler and humidifier before servicing.
- Step 1 – Enable humidifier: In the thermostat installer setup, confirm that a whole-home humidifier is configured and the correct type is selected.
- Step 2 – Check humidity setpoint: Ensure the setpoint is above current indoor humidity and that any outdoor temperature lockout settings are not preventing operation.
- Step 3 – Inspect wiring: At the indoor unit, verify that the humidifier is wired to the correct HUM or accessory terminals as per Trane’s wiring diagram.
- Step 4 – Test output: In installer test mode, command humidifier ON and measure for 24 VAC at the humidifier control terminals.
- Step 5 – Check humidifier hardware: If voltage is present but no operation, the humidifier solenoid or internal board may be faulty and require replacement.
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Repair Difficulty
Hard
4/5
Required Part
Trane Whole-Home Humidifier or Trane Smart Thermostat
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