Your boiler has detected a problem with its internal temperature sensors, meaning it cannot accurately monitor the water temperature and has shut down as a safety precaution.

Flow or return sensor fault. Short circuit in the flow, return or boiler temperature sensor. Defective or not (properly) connected flow, return or boiler temperature sensor.

What causes this fault?

This fault occurs when the boiler's internal computer loses communication with the sensors that monitor water temperature. It is usually caused by an electrical failure within the sensor itself or a loose connection in the wiring, preventing the boiler from knowing if it is safe to continue heating.