Thanks Aptsys
...which was kind of going to be my next question - yes, I found this and it does indeed shut off the hot water feed - Thanks
Hot water cylinder with a cold water storage cistern above it.
Cheers,
W.
...it's on the hot inlet to my bath tap (and I am wanting to replace the bath...). No other isolation valve apparent between immersion and tap. A hex key in the inner opening just rotates as if worn, the outer is more than twice the size of any hex key I have and although the outside is...