Thermostat shows E203 and indicates communication error with one or more zoning dampers or zone control module.

Safety warning: Turn off power to the HVAC system and zone panel before servicing.

• 1. Verify zone panel power:
  • Locate the Lennox zone control panel (often near the furnace/air handler).
  • Confirm its LED indicators are lit when powered.
• 2. Inspect damper wiring:
  • Check each zone damper connection at the zone panel for loose plugs or broken wires.
  • Ensure polarity and terminal labeling (e.g., M1/M2, open/close) match Lennox documentation.
• 3. Isolate a faulty damper:
  • Disconnect one damper at a time and power cycle the system.
  • If E203 clears when a specific damper is disconnected, that damper or its wiring is likely faulty.
• 4. Verify thermostat zoning configuration:
  • From the Lennox smart thermostat menu, review zone setup.
  • Ensure the number of zones and damper assignments match the physical installation.
• 5. If communication errors persist:
  • The Lennox zone control board may be defective.
  • Have a qualified technician test and replace the zone panel if needed.