Exactly what has just happened to my Impulse shower, Here is the address of the part page cost £21 ish. Cheaper than a new shower . There is a pin that holds the water control and heat dial in place - this snaps and the dial just spins or jams. http://www.shower-warehouse.co.uk/erol.html#1083x0&&http%3A%252F%252F for details of the shower look at www.showerdoc.co.uk%252Fshower-spares%252Fgainsborough%252Fimpulse.html
The only solution I think is to buy a new front cover part number 95.614.193.
Thats what I am doing anyway.
Andrew Scott
April 2008