no probs thanks, i googled it there and there is a step by step guide on how to fix without buying a new prd..
1. Turn off electrical supply to shower at the main fuse board.
2. Unscrew the hose from the bottom of the shower unit.
3. Remove the casing screws (2 on top of cover, 1 under the cover).
4. Set the temperature control dial to the mid-blend position and remove, this will ensure ease of re-fitting the dial.
5. Remove the front cover, by tilting the top of the cover towards you and sliding it downwards.
6. On the left hand side you will see the white plastic outlet pipe. (This is where your hose screws onto).
7. Using a crosshead (Phillips head) screwdriver- remove the small fixing screw that secures the outlet pipe to the black heater tank and twist the outlet pipe whilst pulling it gently down.
8. Carefully remove the outlet pipe from the heater canister.
9. Approximately 1 inch above the threaded end of the outlet pipe is a small tee-junction which should contain a small silicone ball, push the white cap covering this ball upwards with a screw driver to gain access to the ball.
10. Using a blunt instrument (back end of a biro pen for example), push the silicone ball back into the housing until it locates firmly. (Note: the ball will not push all the way through into the outlet pipe).
11. Re-fit the outlet pipe ensuring that the tee-junction is facing the wall and that the o-ring seals correctly into the heater canister.
12. Re-fit the front cover, control dial and hose.
13. Remove the shower head from the hose and point the open end into the shower tray or bath.
14. Turn the shower unit on and ensure that water is not escaping from the PRD. If this is fine, reattach the shower head and test again.
15. Re-instate the electrical supply.