On Thu, 20 Aug 2009 16:46:23 +0100, "Toby"
wrote:

Well, you don't need to drain the hot tank, just drain the cold,

That's true but how would you do this without making a mess? The only
way I can think of is by bailing out the tank with buckets or
siphoning it but that requires getting to the tank in the loft. The
problem is that no-one has been in the loft for years, there's no
lights up there and no boarding, so it's an expedition I would like to
avoid if possible! I'm still hoping there will be a valve in the
airing cupboard

If it were me, I would install a full bore lever valve like this if I were
draining stuff down, for the future...
http://www.screwfix.com/prods/17293

NOT one of these
http://www.screwfix.com/prods/18334

Also, where you are working under the sink, install some of these if you can
http://www.screwfix.com/prods/76597

All good stuff that I've fitted to my home already

And if you are doing all of this, make sure the mains water shut-off is
elderly relative friendly too - installing a lever valve is a hell of a lot
easer to use than a traditional stop cock

One of these is even easier (although I have not used one myself yet, I have
had good feedback from someone who has one)
http://www.surestop.co.uk/

I bought one from Tool station and in an emergency it's much faster
than clearing a path to the stop cock and frantically turning it!

Thanks again.