fitted new bathroom suit with new shower , there was already a pump under the bath for the existing mira mixer shower. pump does not start when shower is turned on. its one of these ocean multy jet with loads of buttons and two shower heads but there is only water coming out at a slow rate.both hot and cold come from the storage tank.i have check the fuse, with no luck.have i forgot to do something or could there be a fault with pump. customer says it was working fine before.could the new flexies on this new shower unit reduced the flow so the pump does not kick in.