Hi John, need some more detail, but to check the Flow/Stabiliser valve, remove handset and turn from full cold to full hot, there should be a marked difference. Also check the inlet valve and any valve on the supply plumbing is fully open. Empty the circular Scale Trap to the left of the outlet pipe.
This is one of those showers that works well but also can be problematical, hope that helps
Keith Totally Showers, May 2013
