Our water pump packed up whilst we were away recently - absolutely zilch when you turned on any of the 3 taps (Kitchen, bathroom, shower) or pressed the toilet flush.
When turning on the 'pump' switch on the control panel, you could hear a faint click in the Calira charger unit as the relay closed.
I measured the voltage on the 'Pump' connection on the distribution box (Connection 18 in the attached diagram), and verified that there was +12v present (well, +14v as the leisure battery was fully-charged), and also that this came and went with opening taps.
Everything was pointing to the pump.
We dropped into Oxford Caravan Centre
on our way home. They had two 'high volume immersion pumps' in stock - a Truma at £45 and a Whale at £35. They weren't able to say which was better, so I bought the Whale (and I'm glad I did, see later).
The fresh water tank is under the bench seat at the front, and the power lead disappears off under the inlet pipe (see photo).
To get at this you have to remove the lift-up seat (8 screws), which then lets you access the cabling. You need skinny arms, but the power lead from the pump is connected to a 'chocolate block' connector and is held steady by a retaining clip screwed to the floor.
Removing this retaining clip let me pull the chocolate block connector up enough to get a multimeter on it and to verify that power was reaching that point too (ie there wasn't some other damage to the internal wiring).
By removing the big red screw-in inspection cover, undoing the jubilee clip retaining the blue hose, and the retaining nut for the red elbow tank connector, the whole pump can be manoevered out through the inspection hole in the top of the tank.
This is where buying the Whale became a good idea, as its outlet is at the top rather than the bottom, so all I had to do was trim down the blue food-grade hose from the original pump to fit the new one.
I didn't take a photo of it before I removed it, but there was a length of semi-rigid white plastic pipe sleeving the blue food-grade pipe (presumably to help keep it rigid). This too needed trimming by an inch or so.
In order to get the blue food-grade pipe to fit over the outlet from the Whale pump I softened it by immersion in a boiling kettle for a minute or so.
Finally, the whole assembly can be manoevered back into position, outlet and power cables re-connected, and the red elbow tank-connector tightened up.
The Whale replacement works fine and seems to be of comparable power to the Knaus original.