Display shows E03 and the thermostat reports no temperature reading; room temperature shows as ‘--’ or 0°C.

Safety: Do not open the thermostat housing or access internal electronics unless you are qualified. Low voltage is present but improper handling can damage the unit.

• Power-cycle the system: Turn off power to the heating control module at the boiler’s isolation switch or circuit breaker for 30 seconds, then restore power and check if E03 clears.
• Check for extreme conditions: Ensure the thermostat is not exposed to condensation, direct water spray, or extreme heat sources that may have damaged the sensor.
• Reset to factory defaults: From the thermostat menu, perform a factory reset (note: this will erase schedules and Wi‑Fi settings). Reconfigure and see if the sensor reading returns.

If E03 persists and the temperature still reads ‘--’, the internal NTC sensor on the Ngenic thermostat PCB is likely faulty. The thermostat front unit typically needs replacement as a whole assembly.