I don't have a Westy with a sink and faucet so I don't fully understand all things involved.  I DO know that good ole cheap white vinegar (mild acid) is great for slowly loosening and dissolving mineral buildup and deposits on parts such as these.
Just an idea.
RichSan Diego

      From: David McNeely <davmcneely40@GMAIL.COM>
 To: vanagon@GERRY.VANAGON.COM 
 Sent: Saturday, January 20, 2018 3:18 PM
 Subject: Re: Where best to check my Westy water system?
   
In tank pump in my 1991 Volkswagen Vanagon GL Campmobile stuck so no flow.
Level float also stuck.  Both ok after manipulation by hand and for the
float cleaning the wand.  Stuck pump has happened more than one time.  For
both, probably a little biofilm buildup, though I do use bleach in the tank
periodically.  mcneely

On Sat, Jan 20, 2018 at 12:55 PM, turbotransporter <ramblinvan@gmail.com>
wrote:

> They will sometimes get stuck if not used for a while... surprisingly they
> will hum but not blow the fuse.
>
> Sent from my way cool iPhone.
>
> > On Jan 20, 2018, at 12:36 PM, Tom Buese <tantonbz@GMAIL.COM> wrote:
> >
> > In tank pump is dead?
> >
> >> On Jan 20, 2018, at 3:31 PM, Jim Felder <jim.felder@GMAIL.COM> wrote:
> >>
> >> Today it warmed up a lot so I checked out a few things on my westy
> (1983). I discovered that my faucet switch had no effect. I pulled the knob
> and shorted the contacts to make sure the switch was closing. No effect.
> Measured the voltage between contacts. Zero. The lights in the panel are
> working, fuses are all good.
> >>
> >> Any recommendations?
> >>
> >> Thanks,
> >>
> >> Jim
>