Your boiler has stopped working because it can no longer communicate with the sensor that monitors the temperature of the main heating unit.

Heat exchanger temp sensor disconnected

What causes this fault?

This fault occurs when the boiler's internal computer loses track of the heat exchanger's temperature, usually because the connection to the sensor has broken or the sensor itself has failed. Over time, the constant heating and cooling of the boiler can cause the wiring to become brittle or the sensor to degrade, preventing it from sending a clear signal. Without this safety information, the boiler shuts down immediately to prevent the unit from overheating.