Thermostat displays E1 and will not control heating or cooling

Safety first: Turn off power to the HVAC system at the breaker before removing the thermostat from the wall plate.

• Power cycle the thermostat: Turn HVAC breaker off for 2 minutes, then back on. If E1 clears temporarily and returns, the sensor circuit is likely faulty.
• Remove thermostat from wall plate: Gently pull the Honeywell Home thermostat straight off the wall plate. Inspect the back of the thermostat for signs of corrosion, moisture, or physical damage.
• Check for liquid damage: Look for condensation or water marks around the sensor area (usually near the air vent slots). If moisture is present, allow the thermostat to dry completely (24 hours in a dry, warm room) and reinstall.
• Inspect sensor vent openings: Make sure the front vents are not blocked by paint, dust, or debris. Use compressed air to gently blow out dust.
• Factory reset (if supported): From the thermostat menu, perform a factory reset following the Honeywell Home manual. Reconfigure Wi‑Fi and system type. If E1 persists, the internal sensor or PCB is defective.
• Replace thermostat: If the E1 code remains after drying, cleaning, and reset, the internal temperature sensor circuit is open and the thermostat assembly should be replaced.