update:

This morning, I did finally remove the control knob but had to use two
screwdrivers on either side to lever it off the knob. Limescale I
guess must have caused the knob to be 'seized' onto the end of the
spindle. The gasket had failed, cleaning and refitting didn't totally
cure the big leak but it was better than the water gushing out. (system
is mains water pressure fed)

So bought a new grey cartridge kit which included new gasket/screws etc
from Plumbase for £78.25.


Unfortunately I didnt realise it is also 'recommended' the hot water O
ring should be replaced and I don't fancy taking it all apart to fit it
as it took me ages to refit the inner shroud (I didn't remove the outer
shroud/plate which is siliconed to the wall)

Can someone tell me what the symptoms are for a failed/worn hot water O
ring? I'm not seeing any leaks, or drips from the shower head if that
helps

cheers


bill