RichardS wrote:
"Andy Hall" wrote in message
...
On Sun, 31 Aug 2003 19:16:23 +0100, "Margaret Macfarlane"
wrote:

Hi,

Just found this newsgroup and discovered that there are more than
14,000 headers to download so forgive me if this question has
already been asked
[Snip]

The build up may well be hydrogen gas, rather than air. Hydrogen
is the product of corrosion of metal components in the system. In
addition to the pump, you would expect to find it gathering in the
tops of radiators. You can easily test whether it is hydrogen by
opening a radiator vent and applying a match or other flame.
Hydrogen burns with a pale blue flame.

snip

This is the only part of the advice that I'd disagree with.

When testing for hydrogen I would never advise applying the flame
directly to the vent, but rather collecting in an upturned container,
then introducing a (long) match or splint to the container (still
upturned). A satisfying "pop" should be heard if hydrogen is present.

cheers
Richard
I'd advise caution here too. Heard of a guy who applied match as he opened
rad air bleed valve.
It was combustible gas and the resultant large flame startled him and caused
a large burn mark on his wall.