Shower problem

Back feeding up the cold is all I'll say, you need to have some kind of one way valve and some way to calibrate it I'd say. Also don't use the Home Owners club for posting to usenet many helpful people see so much dross from there they won't see your post. Try eternal September and a proper news client. Brian

sounds like too much hot pressure.

It sounds like you are trying to mix mains cold (at a fairly low supply pressure) with hot from a pumped gravity fed cylinder.

The normal way to do this would be to take a low pressure cold feed from the cold cistern to the shower rather than mains cold. Then use a shower designed for low pressure operation. Alternatively a twin impeller pump can be added to pump both sides.

An alternative would be to fit a venturi shower - these use the cold pressure to assist the hot supply. Probably not going to work with a soaker head though.

Other options would be replacing the hot water cylinder with an unvented one that runs at mains pressure.