The water pump fails to shut off.
Normally it shuts off shortly after closing the water tap, as soon as full water pressure has been restored. But lately it doesn’t. Or at least not reliably. The pump itself doesn’t seem to be the problem, so we suspect the Electronic Pressure Control unit.
Perhaps it’s tiny electronic brain is fried?
After some messing around the water pressure reported by the epc went up a bit, but otherwise there is no observable difference in behavior.
we decided to bite the bullet and order a new electronic pressure control unit.
Luckily the vendor quickly identified th nearest reseller and shipped it for delivery in just a few working days.
The captain applied her plumbing skill and got rid of our not so trusty old epc and installed the new shiny model. 
Despite being much larger it fit all the existing connection without adjustments and functioned as a drop in replacement.
The result is that the water taps can be used again without triggering endless whining of the pump. Jay!
It is still not clear what was wrong precisely with the old EPC… perhaps it reached pension age and gave up on mundane tasks like switching off pumps? It’ll have time to contemplate that and more while resting in the bin of broken parts.