E201
Lennox
Communication Fault Between Thermostat and Furnace Control
Furnace intermittently shuts down; thermostat or board shows E201; system may restart after power cycle.
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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
Loose thermostat terminal connections, Damaged Lennox iComfort communication cable, Faulty Lennox communicating thermostat, Faulty Lennox integrated control board communication circuit
How to Fix / Troubleshooting
Safety: Turn off furnace power before touching wiring.
- 1. Inspect thermostat wiring: Remove the furnace blower door and thermostat cover. Verify all communication terminals (e.g., R, C, i+, i− or ABCD bus on iComfort systems) are tight and correctly landed.
- 2. Check cable condition: Follow the communication cable from furnace to thermostat. Look for staples through the jacket, crushed sections, or rodent damage. Replace damaged cable with the same gauge and type recommended by Lennox.
- 3. Reseat connectors: On communicating systems, unplug and firmly reseat any modular plugs on the Lennox control board and thermostat.
- 4. Power reset: Turn power OFF for 60 seconds, then ON. Allow the thermostat and furnace to re-establish communication.
- 5. Firmware/compatibility: If a new thermostat was recently installed, verify it is compatible with your Lennox furnace model and that firmware is up to date.
If E201 persists after wiring checks, a technician should test the control board and thermostat communication circuits.
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Repair Difficulty
Medium
3/5
Required Part
Lennox iComfort Thermostat
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