In an earlier contribution to this discussion,
Fatboise wrote:


First off, you need to determine whether it *is* air - or hygrogen.
The
latter is caused by corrosion if there is insufficient (or no!)
corrosion
inhibitor in the system. Next time you bleed the rad, collect some
this
'air' in an upturned jam jar and then apply a lighted taper to it. If
it
burns with a blue flame, it's hydrogen.

Can somebody please explain how to test for hydrogen as mentioned
above I'm afraid I don't understand the explanation - D'oh

If you hold a lighted match or taper in the stream of gas coming out of the
bleed hole, you can tell whether it's air or hydrogen by its behaviour. If
it's air it will have no effect, or may even blow the flame out. If it's
hydrogen, the hydrogen itself will burn with a blue flame.

But it might also set fire to surrounding objects - which was why I
suggested doing it in two stages. Because hydrogen is a lot lighter than
air, it will rise - so if you hold a jamjar upside down, with the open part
just above the bleed screw, any hydrogen will collect in the jar. If you
then introduce a burning taper up into the jar, you'll see whether or not
the collected gas burns. If it *does* it will do so in a more controlled
way, without setting fire to the whole house!
--
Cheers,
Roger
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