the solenoid valve was another issue ok.
showerhead not at fault.
the inlet filter must be ok if the solenoid valve was changed.
so my next step would be to check the mains stopcock or any iso valves to the shower.
if all ok.
if all ok i'd check the bottom tco (thermal cutout)
is their any visable burnt wires etc round the bottom tco
hi-spec plumbing & heating (essex), June 2010