On Fri, 02 Mar 2012 18:01:12 +0000, Fredxx wrote:

If you're quick, and I was once, you can remove the radiator valve by
undoing the nut while firmly pushing the valve onto the pipe, then
whipping off the valve with thumb ready to cover the pipe. Use a
reverse operation to place the compression cap on the end of the pipe.
If you're luck and quick you'll lose surprisingly little water.

If you have a normal open vented system bung corks in the vent pipe
and feed from the tank and very little water escapes. Do not have
more than one point in the pipe work open at time, that would allow
air in and water out...

Never had a pressurised system but I should imagine if you de
pressurise completely then seal it back up you can again open one
point at a time.

--
Cheers
Dave.