Thanks for the reply,

I had another look at the set-up last night:

Shower is on the same level as the boiler and is a direct feed from
the hot water (ie not electric).
There is no cold water tank in the loft - is it possible that a) I'm
blind, b) I need a stronger torch, or c) there's one to service
several of the flats?

I also had a closer look at the door problem even letting the door go
from 1" from the closing position is enough to shake the frame - the
frame is connected to the light wooden frames behind the plasterboard
which tend to shake every wall they're connected to.
Is there any where to put nails, screws, or other bits of metal to
stop it doing that?

Cheers
Nick