Your boiler has detected an electrical fault with a sensor that monitors the water temperature flowing into your heating system, leading it to shut down for safety.

Controls without flow temperature sensor (low loss header): System flow temperature sensor shorted out

What causes this fault?

This fault occurs when the electrical signal from the temperature sensor is interrupted or fails to send back the correct information. The most common reason is a physical failure of the internal sensor components or damage to the wiring that connects the sensor to the boiler's main control board. If the boiler cannot accurately measure how hot the water is, it shuts down to prevent the system from overheating.