Your boiler has detected that the water inside the unit has become dangerously hot and has shut itself down to prevent damage.

high limit flow temperature probe

What causes this fault?

This fault occurs when the boiler's internal computer struggles to communicate with its sensors or other electronic components. It is often caused by a brief interference in the electrical signals or a loose connection within the internal wiring that links the parts together. In some cases, it can indicate that the main control board is beginning to fail and is struggle to process information correctly.