Thermostat shows E220 indicating internal temperature sensor fault; room temperature reading is missing or obviously wrong.

Safety warning: Turn off power to the thermostat at the HVAC breaker before removing it from the wall.

• 1. Reboot the thermostat:
  • Power down the system for 2–3 minutes and restore power.
  • Check if the temperature reading returns to normal.
• 2. Inspect for environmental issues:
  • Ensure the thermostat is not installed above a heat source, in direct sunlight, or near drafts.
  • Look for signs of water damage or condensation on or behind the thermostat.
• 3. Remove and reseat thermostat:
  • Gently pull the Lennox thermostat off its wall base.
  • Inspect the pin connector for bent or corroded pins; clean gently if needed.
  • Reinstall firmly and ensure it snaps into place.
• 4. If E220 persists:
  • The internal sensor is likely failed and not field-repairable.
  • Replace the thermostat with a compatible Lennox smart thermostat model.