Water pump problems

[RoggyDoggy]

Hi, I have a 2000 Avondale Landranger 6400FB (Millenium Edition), I've owned it for a few months now.
The van has an internal water pump for an internal tank. It also runs an external pump to 'top up' the internal tank.
My problem is that the internal pump does not appear to work and the external pump, when turned on, operates every 7 seconds or so even if all taps are turned off.
We have the instruction manual for the water system and all switches / valves appear to be set as required.
I guess that the 7 second operation of the pump is governed by a relay somewhere but I'm unable to hear one operating.
Does anyone have any suggestions as to why A) the internal pump doesn't appear to work and B) why the external pump operates as it does?
Any schematics would be a great help.
Thanks

 

[Damian]

The internal pump may simply have failed and need replacing.
The external pump by the sound of things is governed by a pressure switch, when the pressure drops, the pump runs.
If it is cycling as you indicate, that usually means a leak somewhere.

 

[chrisn7]

Usually the external and internal pumps are the same type, so that if the internal has been left on with insufficient water in the tank it will have run until it failed as these pumps cannot be run when dry.....