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. There was no retention screw as advised. The leak was due
to the gasket having failed, cleaning and refitting didn't totally cure
the problem but it was better than the water previouslyl gushing out.
(system is mains water pressure fed)

So I 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 again 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 usual 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. Everything appears to be working as normal but it is
early days....

cheers


bill