Your boiler is experiencing a communication problem with its internal temperature sensor, causing it to shut down unexpectedly from time to time.

Intermittent lock-out

What causes this fault?

This fault occurs when the boiler's main control board loses its connection with the temperature sensor that monitors the heat exchanger. The most common reason is that the sensor has developed an internal electrical failure or the wiring connecting it to the circuit board has become loose or corroded over time.