Your boiler has stopped working because a sensor that monitors the water temperature has developed an electrical fault.

Burner blocked. Short circuit - outlet temperature sensor.

What causes this fault?

This fault occurs when the sensor responsible for measuring the hot water leaving the heat exchanger develops an electrical short circuit. The most common reason is internal component failure within the sensor itself or moisture ingress damaging the electrical connections. Because the boiler can no longer safely monitor how hot the water is getting, it shuts down to prevent overheating.