Trane
Heating Call Not Reaching Indoor Unit
Thermostat calls for heat, but the furnace or air handler does not start.
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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
Open W1/W2 circuit between the thermostat and Trane indoor unit, failed thermostat heat output relay, loose W wire at the control board, safety lockout on the furnace preventing heat
How to Fix / Troubleshooting
Safety warning: Turn off power to the furnace/air handler before opening panels.
- Step 1 – Confirm heat call: Set the thermostat to HEAT and raise the setpoint. Verify that the thermostat shows a heating demand.
- Step 2 – Measure W voltage at thermostat: With a multimeter and an active call, measure between W1 and C. You should see ~24 VAC.
- Step 3 – Check W at indoor control board: At the furnace/air handler, measure between W and C. If no voltage, inspect the thermostat cable and connections.
- Step 4 – Inspect furnace status lights: Many Trane furnaces have diagnostic LEDs. If the board is in lockout, follow the fault code chart on the furnace door.
- Step 5 – Reset furnace: Turn power off to the furnace for 5 minutes, then restore power to clear lockouts.
- Step 6 – If the W signal is present but no heat: The furnace control board, gas valve, or electric heat relays may be faulty and require professional service.
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Repair Difficulty
Hard
4/5
Required Part
Trane Smart Thermostat or Trane Indoor Unit Control Board
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