E03 displayed and thermostat shows room temperature as “--” or extremely high/low values

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

• Step 1 – Reboot and reset:
  • Power cycle the thermostat by turning off the breaker for 1 minute.
  • After power is restored, check if E03 clears.
  • If not, perform a factory reset from the settings menu (note: you will need to reconfigure Wi‑Fi and schedules).
• Step 2 – Check for environmental issues:
  • Ensure the thermostat is not installed above a heat source (radiator, TV, direct sunlight) or in a drafty location.
  • Check for condensation or visible moisture on or around the thermostat.
• Step 3 – Inspect internal sensor (advanced):
  • With power off, remove the thermostat from the wall plate.
  • Locate the small NTC temperature sensor on the front side of the main PCB (often near ventilation slots).
  • Look for broken leads, corrosion, or physical damage.
  • If you have a multimeter and the service manual, measure the thermistor resistance at room temperature and compare to spec.
• Step 4 – Replace thermostat if sensor is defective:
  • The internal ambient sensor is typically soldered to the main PCB and not user‑replaceable.
  • If the sensor is open/shorted or E03 persists after reset, replace the entire thermostat or main control PCB assembly.