There is water coming from the shower overflow on my Gainsborough electric shower(9.5kw).It does not come out from the overflow if we leave the shower head and hose at quite a low level, but as soon as we lift up the shower head to chest height...the pressure drops and the water begins to come from the overflow???Is this something to do with a pressure release valve(whatever that is) or could there be an air lock in my water system?

Streve Hunter, January 2008

it's the prv yes. check your hose or shower head for limescale or the hose for kink.
this is the common reason why they activate restricted flow.

hi-spec plumbing & heating, January 2008