Did you find a tiny black ball in the shower, the size of a letter "O" this has come out of the "pressure relief device" which is a small white plastic "T" shape fastened by two screws. You will find it inside the unit just behind the outlet hose. It has it's own little bit of outlet tube. The device needs to be renewed. Don't throw any parts away until you get the new ones. Checkout National shower spares
mick, January 2013
