Micro switch problem.
We have ad the wire break twice in the last 2 years. The wire breaks so that no hot water comes out of the tap in the kitchen once the pressure has gone. The bathroom is ok and the toilet water is fine so the pump is ok.
We even met a couple in Germany with the same fault. The micro switch in the tap switches the pump on when the tap is opened.
The wire is quite brittle and eventually breaks. I have re soldered the cable and I am going to replace the wire with 0.5 mm 11A 12V flexible cable next time it fails. I did the video below just to show how to get access to the wire.