sounds like a solenoid valve fault.
but you don't give enough info.
hi-spec plumbing & heating (essex)
May 2010
did it work before? if not check its connected to mains cold water not tank water failing that a valve could have seized inside the shower or the capillary pipework has become blocked by hard water. i would recommend gettin a plumber if its a valve or a blockage
ahplumb
May 2010
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