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

Short circuit – flow–NTC (< 130 °C) | Cause: NTC– plug shorted to casing, NTC defective

What causes this fault?

This fault occurs when the boiler's control board receives an incorrect electrical signal from the sensor that monitors the temperature of the water leaving the unit. The most common reason is that the sensor has failed internally or the protective coating on the connecting wires has worn away, causing an electrical short circuit. When the boiler can no longer accurately track the water temperature, it shuts down immediately as a safety precaution.