Your boiler has shut itself down as a safety precaution because one of its internal safety sensors has detected a potential fault.

REFHI TOO HIGH ERROR Temperature measured not correct

What causes this fault?

This fault occurs when the boiler's internal safety switches detect that the unit is operating outside of safe temperature or pressure limits, triggering an immediate shutdown to prevent damage. The most common reason is a failure in the safety thermostat or the flue sensor, which may be sending incorrect signals to the control board. It can also be caused by a communication error within the internal wiring or the main circuit board itself.