Your boiler has detected a problem with its internal temperature sensors, which means it cannot accurately monitor the water temperature and has stopped working for safety.

Sensor fault S2

What causes this fault?

This fault occurs when the boiler’s return sensor, which monitors the temperature of the water coming back from your radiators, sends an incorrect or missing signal to the main computer. The most common reason is that the sensor itself has developed an electrical internal failure, or the wiring connecting it to the control board has become loose or damaged.