Control panel

[Kitch1st]

The water pump will only work if I also switch the grey water tank heater on which rapidly drains the power from the leisure battery.

 

[meanders]

Hi and welcome. You need to post the make, model and year of the van. That's the converter make, Hymer, Eldiss, Autotrail etc,

A picture of the control panel may also help people to help you.

I suspect there may be a problem with the wiring. Has the pump been replaced?

 

[Kitch1st]

It is a Swift A521 Lunar Champ first registered Feb 2007. I don't know if pump has been replaced as I have only recently purchased the vehicle.
Photo attached.