"Christian McArdle" wrote in message
et...
Nope, but it might have started when I did some other work on
the dhw pipes - that was very soon after we got the boiler in,
and I couldn't swear it did/didn't happen before that.

Then it sounds like an airlock to me. Do you have any inverted U shapes in
the pipework? Perhaps a manual bleed valve at a convenient location would
help.

There *could* be a slight airlock in one place if the pipe isn't quite
horizontal,
but it's downstream of the tee to the shower, so shouldn't cause issues with
that.

Presumably the boiler ought to have some kind of automatic venting, given
all pipes lead down from it.

You know, it's just occurred to me that a compression joint doubles up
quite well as a bleed valve

I'm a little surprised, though. Normally, mains pressure can blast through
airlocks (indeed the normal solution to one is to connect it to mains
water), so it would have to be a biggie.

I haven't run the hot water at full flow for a while, so I'll try that for
a few minutes tonight and see if anything changes. Failing that I guess I'll
be having a nose inside the boiler to see what's it looks like.

Ben