Your hot water system is getting too hot and has shut down as a safety precaution.

D.H/W sensor overheating error

What causes this fault?

This fault occurs when the internal temperature sensor detects that your hot water is becoming dangerously hot, triggering an emergency shutdown to prevent scalding. The most common reason is a buildup of limescale or debris inside the heat exchanger which restricts water flow, but it can also be caused by a mechanical failure in the diverter valve or a faulty sensor giving a false reading.