How to Fix / Troubleshooting

Safety: Turn off power to the indoor unit before changing dip switches or control boards.

1. Verify equipment configuration: Access the Lennox thermostat installer menu and confirm the correct indoor and outdoor model numbers are selected.
2. Check dip switches/jumpers: On the indoor control board, verify airflow and tonnage dip switches match the installed equipment per the Lennox installation manual.
3. Re-run system setup: Many Lennox communicating systems allow an auto-discovery or setup routine. Run this to let the thermostat detect connected equipment.
4. Confirm component compatibility: If a control board or coil was recently replaced, ensure the parts are approved for use with your specific Lennox condenser model.

Note: Configuration errors can cause improper airflow and staging, reducing efficiency and comfort.

Lennox communicating system shows E440 indoor unit configuration or model mismatch error; system may not operate or may run in backup mode.

Possible Causes