"Johnny" wrote in message
...
Thanks for the replies everyone.

I've decided to leave the mains water turned off, as I can't be 100%
certain
that it's the hot water cylinder that's leaking - it could be one of the 4
pipes that run from the attic down through the floor and may be leaking
under the airing cupboard floor (I have a total of 7 pipes coming from the
attic into the airing cupboard)

Also, the other reason why I was concerned about whether it's safe to
leave
the pilot light on the central heating boiler is because (after looking at
drawings in DIY books etc) there seems to be pipes that enter the hot
water
cyclinder - even though I can have hot water without the CH being on and
vice versa.

You can tie up the ball-float valve on the big tank in the attic which'll
stop the HW system getting any water, then you can turn back on the mains
stopcock to get cold drinking (and cold washing and flushing the bog) water.
You can run your CH system too, but set the programmer for HW OFF otherwise
it'll try in vain to heat up the non-existent water in the cylinder until
the cylinder thermostat says it's hot enough. Won't do any harm but a waste
of energy.