Managed to get to the bottom of this problem - some updates.
1. My mains pressure was checked and found to be 8 bar (no problems here).
2. Thought my pressure was too high so I partially closed the stopcock - made no difference.
2. Called Gainsborough service agent fitted another new...
This is a real strange one - about a month or two ago my 18 month shower started playing up - problem was very low flow/pressure when temperature turned up to warm (not even hot). Gainsborough sent me out a replacement engine (inside parts) which I fitted, but problem remained. Engineer then...