Your boiler has stopped working because an internal temperature sensor is reporting an error and needs to be checked.

Sensor S0 is defective.

What causes this fault?

This fault occurs when the boiler's main internal temperature sensor fails to send a consistent electrical signal back to the central control board. The most common reason is that the sensor has suffered a physical failure or the wiring connecting it has become loose or damaged over time. Because the boiler can no longer accurately monitor how hot the water is, it shuts down as a safety precaution to prevent overheating.