Your boiler has stopped working because it thinks the main water temperature sensor is broken or there is a problem with its internal wiring.

Short-circuit in feed temperature sensor: Sensor plug has mass short to the casing, short-circuit in wiring loom, sensor faulty

What causes this fault?

This fault occurs when the boiler's control board detects an electrical short-circuit coming from the main temperature sensor. It usually happens because the internal components of the sensor have failed or the insulation on the connecting wires has worn away and touched the metal casing. Because the boiler can no longer safely monitor how hot the water is getting, it shuts down as a safety precaution.