Thermostat displays E1 and will not control heating or cooling

Safety first: Turn off power to the HVAC system at the breaker panel before removing the thermostat from the wall plate. This prevents short circuits and protects the control board.

Steps to try:

• Power cycle the thermostat: Turn HVAC breaker OFF for 2 minutes, then ON. Remove the thermostat from the wall plate for 30 seconds and reattach. If E1 clears and does not return, monitor operation.
• Check for moisture or contamination: Remove the thermostat from the wall. Inspect the front housing and visible circuit board for signs of condensation, corrosion, or insect debris. If you see moisture, allow the thermostat to dry in a warm, dry room for several hours (do not use a hair dryer or oven). Reinstall and test.
• Stabilize ambient temperature: If the thermostat is installed in a location with extreme drafts (direct supply vent, exterior door, or window), temporarily shield it from direct airflow and see if the error clears after a power cycle.
• Factory reset (if supported by your Sensi model): Use the app or on-screen menu to perform a factory reset. Reconnect Wi‑Fi and reconfigure system type. If E1 persists immediately after reset, the internal sensor is likely failed.

When to replace: The indoor temperature sensor is integrated into the Sensi main control board and is not field‑replaceable as a separate component. If E1 persists after power cycling and drying, the thermostat assembly should be replaced.