On Fri, 18 Mar 2005 00:29:01 +0000, John Stumbles
wrote:

snip original post

I assume you mean the gate valve in the pipework from the storage tank
in the attic feeding into the bottom of the hot water cylinder as this
is the usual position for a valve to stop the hot water supply. You can
stop the flow to this valve in order to change it by blocking the outlet
from the tank. Usually this will be 22mm (maybe 28mm: if it's 15mm
something is wrong) and the traditional stopper is a carrot :-) Drayton
sell rubber bungs for this sort of purpose (but they're expensive). Wine
corks are the wrong size although IIRC those rubber vacu-vin stoppers
might do. Just don't even think of plasticene or blu-tack: it's liable
to get sucked into the pipework!

I always replace gate valves with lever-operated full-bore ball valves
like http://www.screwfix.com/app/sfd/cat/pro.jsp?id=17293
You need to cut back the pipe to accomodate these valves as they have
longer bodies than gate valves.

You might have to get off the old olives and nuts to put a new valve on
anyway as sometimes the old valve has different threads on its
compression nuts than new ones. Sometimes you can persuade the old olive
to slide off by tapping the back of the nut but if not you saw carefully
through the olive using a junior hacksaw almost parallel to the pipe
direction and then splittingthe olive with a screwdriver blade.

You might also find that the old pipework is 3/4" rather than 22mm in
which case you really should use 3/4" olives (designed to work in 22mm
fittings to adapt to old pipe) though I have got away with tightening up
a copper 22mm olive a long way.

The carrot trick was nothing short of briliant! It worked, the valve
is replaced and hot water is restored.

Think I'll replace the others before this happens again...

Many thanks to all.