On Mon, 06 Sep 2010 19:22:56 +0200, rbel wrote:

Are these bungs any good?

They work, provided you only have one opening into the system at any
given time. Two opeings and the chances are air will go in one and
(yukky) water come out the other even if they are nominally at the
same level.

We want to change radiators (to more modern compact design units) ...

If the existing rads have valves each end and the new rads will fit
into the same length space you needn't bother with the bungs, just
shut the valves but remember that the rad is still full of water...

If you need to adjust the pipe work you might get away with the bungs
but I'm not sure I'd risk it. The pipe waggling or cutting into a
horizontal run may well let air glug in and water out.

--
Cheers
Dave.