ive just had this problem ,check inlet valve isnt blocked, if not check the resistance measurement on the solienoid valve with multimeter the two contacts at the bottom should read 3.85, if its 000 it needs replacing cost about £10.00 from triton. its just as easy to take shower off the wall to do it 20min work, check to see if you need a stabilizing valve aswell .its sits above solienoid valve, this might be leaking, you will only no if you remove the front cover then turn it on.
kazcmot, February 2006