In article ,
Victoria wrote:
We've asked our IoP registered, corgi plumber back but he's claiming
it's nothing to do with him. He says the knocking is from the old
system and the rad doesn't heat up because of the pipe size or maybe
sludge in the system. He never mentioned pipe size when he was
fitting our boiler, rads and cylinder. And as replaced all rads and
rescaled the system I wouldn't expect any sludge.

Did he make any recommendations - like replacing the pipework - at the
time of giving his estimate?

If not, since he changed the rads, it's not unreasonable to expect them
*all* to work.

Sounds like the threat of a small claims court might get him off his a**e.

However, two things are likely.

One is an airlock. Have you tried bleeding the rad to make sure there's no
air in there? If water doesn't immediately come out under pressure and
there's no air either it could well be an airlock.

Next, as has been said, is balancing the system. If you turn off all the
other rads and this one now works, then this is probably the cure. See FAQ
for details of how.

http://www.diyfaq.org.uk/

--
*I get enough exercise just pushing my luck.

Dave Plowman London SW 12
RIP Acorn