"charles" wrote in message
...
In article , harryagain
wrote:

"charles" wrote in message
...
I was getting localised boiling (kettling) in my GlowWorm boiler when
the pump turned off. I've added ScrewFix Boiler Noise Reducer and that
problem seems to have gone. I now get an alarming clanking instead
which I'm sure wasn't there before.

Any ideas as to what is causing it and how to stop it?

Could be airlock but sludge is also a possibility causing local
overheating. Clanking is caused by steam bubbles forming and collapsing.
(Boiler is still hot, water circulation has stopped) Causing the pump to
run on after the boiler ceases firing is a "fix". (You can try this to
prove the cause)

This is not steam bubbles, I've got rid of those.


You might think you have.


There is pump overrun .

Boiler needs to be flushed out, ideally by removal and hose pipe applied
outside in the garden.

It was power flushed two years ago.


A con, "power flushing" has very little effect.