In an earlier contribution to this discussion,
wrote:

It stopped working, suddenly, about a week ago. At that point the
header tank (5 gall) seemed to be empty or, at least, too low for me
to reach its base (it's rather inaccessible). I replenished it to
about 2/3 capacity.

Have just checked the tap feeding from it. It wasn't fully open but is
now.

The airlock sounds a likely possibility. Can it be cleared without
disconnecting anything?

I'll run the system again now to see if it clears itself but, if not,
I'll wait for your further advice.

Many thanks for your help so far.

Tony.

Hopefully it will purge itself and then be ok.

It's quite a common problem for the ballvalve on the F&E tank to seize up
through lack of use - then when some of the water evaporates or leaks, it's
not replenished - and the level drops enough for the gravity circuit to get
air in it. The pumped radiator circuit often continues to work.

If it doesn't purge itself, you may be able to refill it from the bottom. Is
there a drain cock near (or on) the boiler? If so, you may be able to attach
a hose to that - with the other end connected to a mains cold water supply.
Attach the hose, open the drain cock and then *gently* open the cold tap -
with someone up in the attic watching the F&E tank to ensure it doesn't
overflow.
--
Cheers,
Set Square
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