Thermostat displays E8 and ignores temperature setpoint changes

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

Steps to attempt:

• Normalize environment: Ensure the thermostat is not exposed to direct sunlight, a fireplace, or a supply register blowing directly on it. If it is, temporarily shield it and allow 30–60 minutes for the reading to stabilize.
• Power cycle: Remove the thermostat from the wall plate for 1 minute, then reattach. Also cycle the HVAC breaker OFF for 2 minutes, then ON. Check if E8 clears.
• Factory reset: Use the Sensi app or on‑screen menu to perform a full factory reset. Reconfigure the thermostat and reconnect to Wi‑Fi. Observe whether the error returns.
• Compare with a reference thermometer: Place a reliable digital thermometer near the thermostat and compare readings. If the Sensi reading is wildly inaccurate (e.g., off by 10°F or more) and E8 persists, the internal sensor is likely damaged.

When to replace: The internal sensor and calibration data are not user‑serviceable. Persistent E8 after environmental corrections and reset typically requires replacing the thermostat.