Your boiler has detected an issue with the sensor that monitors the water temperature inside your unit, which has caused it to stop running for safety.

Boiler internal fault (primary sensor fault)

What causes this fault?

This fault occurs when the boiler's main temperature sensor fails to send a reliable electronic signal to the control board. It is usually caused by the internal components of the sensor wearing out over time or the electrical connections becoming loose or corroded. Because the boiler no longer knows how hot the water is, it shuts down immediately to prevent the system from overheating.