This is a common problem and belting either the underside of the tank
or the top of the pump will normally get it working, so I dont think it
will be a relay problem.
I have heard that you can remove, strip and clean the pump as it is
gunging up that can cause the troubles.
Got to be worth a try, I would as you have nuffin to loose.
Try Peugeot for a new one, a Citroen dealer I knew used to buy them in
from Peugeot cheaper than he could get them direct from Citroen, but
the part is the same and in the same box, crazy !! He used to sell them
to me for about £95 + vat, but this was a few years back.
Or you could allways try M&C Lockwood in Bradford, better than GSF they
deal with mail order on Citroen bits 01274 640590
GSF list the Xsantia pump at £135, but list the 306 lift pump (+ sender) at