TritonT80si shower water comes out errratic as if turning a switch on & off?

I have relacated and Moved House from a flat to a 3 bed Bungalow and moved my Triton T80si shower and when switching on the shower the neon light on the mains shower pull switch it keeps flashing on and off in unison with the shower neon flashing on and off also the water from the shower is pulsating as if you were switching it off and on we have taken the water feed directly from the mains cold water pipe and when we disconnected the water pipe to see if there was enough water flow it really gushed out and seemed enough pressure there! my friend felt that there could be an earth leakage some where ?
any suggestions