"David Hansen" wrote in message
...
On Tue, 22 Nov 2005 14:54:48 -0000 someone who may be "Set Square"
wrote this:-

When you open a hot tap, water flows from a cold header tank (probably in
the attic) into the *bottom* of the hot water cylinder, pushing water out
of
the *top* connection of the cylinder - which feeds the taps. So, to turn
off
the hot water, you need to stop water flowing from the header into the
bottom of the cylinder. Hopefully there is a tap or gate valve in the
feed
pipe which goes to the bottom of the cylinder. If so, turn it off. If
not,
you'll either have to tie up the ball valve on the header, and let all
the
hot water run away until it empties the header and stops running - or
you'll
have to interrupt the flow in some other way.

In a sensible plumbing system, where both hot and cold (other than
in the kitchen) taps are fed from a "cold header tank", it is easy
to avoid running all the hot water to waste. Turn off the mains
feed, or tie up the ball valve, then open a cold tap (other then the
one in the kitchen). The water in the "cold header tank" will run
away. After it has stopped, turn on the kitchen hot tap and a small
amount of hot water will run to waste, but most of it will remain in
the cylinder.

Such systems may not be fashionable amongst some, but they do have
advantages.

They are simple reliable and no moving parts. That's all. They are useless
for showers, take up much needed space, use a lot of pipework, can
accumulate debris and the occasional dead rodent in the cold water tank.

I recall a South African friend when we both went into the loft of his new
house. There was water tank. He said "what's that?" I said "the cold water
tank". He replied, "that's going out, this is no farm".