Lennox
No Heating Call Output
Thermostat calls for heat but the furnace or heat pump does not start; no error code shown on thermostat.
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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 wire between thermostat and Lennox furnace/air handler, Failed W output in thermostat, Incorrect heat source configuration (heat pump vs. gas furnace), Blown low-voltage fuse on Lennox control board
How to Fix / Troubleshooting
Safety warning: Shut off power to the furnace before accessing the control board.
- 1. Confirm thermostat settings:
- Ensure HEAT mode is selected and setpoint is above room temperature.
- 2. Inspect W wiring:
- Check W1/W2 connections at thermostat and Lennox control board.
- Look for broken or loose wires.
- 3. Test heat from control board:
- With power on, briefly jumper R to W1 at the control board.
- If the furnace starts, the thermostat or wiring is suspect.
- 4. Replace thermostat if W output is failed:
- If wiring is good and heat works when jumpered, replace the Lennox thermostat.
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Repair Difficulty
Medium
3/5
Required Part
Lennox Smart Thermostat
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