Thermostat displays E4 and indicates a problem with the internal temperature sensor

Safety: This is a low-voltage device; no high-voltage exposure at the thermostat. Do not open the thermostat housing beyond removing it from the backplate.

• Step 1 – Reboot the thermostat: Pull the ecobee off its backplate for 30 seconds, then snap it back on. Allow it to fully boot and check if E4 clears.
• Step 2 – Check for environmental issues: Ensure the thermostat is not installed above a humidifier, kettle, or in direct sunlight, which can cause condensation or overheating. Relocation may be necessary.
• Step 3 – Compare readings: Use a separate room thermometer and any connected SmartSensors to compare temperature readings. If the ecobee’s internal reading is clearly wrong or missing while sensors are fine, the internal sensor is likely failed.
• Step 4 – Update firmware: Ensure the thermostat is connected to Wi‑Fi so it can receive the latest firmware, which may correct sensor calibration issues.
• Step 5 – Replace thermostat: If E4 persists and internal readings are invalid, the internal sensor assembly is not field-repairable. Replace the ecobee thermostat.