On Thu, 30 Oct 2003 11:52:22 +0000, Tim wrote:

"xEcute" wrote in message ...
If you live in an hard water area the banging is almost certainly what is
known as "Kettling". This is caused by a build up of chalk/lime inside the
boiler.
Thanks for the comments but I am not sure they apply to me, I have
tried to explain why.

Well I do live in a hard water area *but* bearing in mind that the
CH/HW is pretty much a sealed system, unless there are leaks and thus
constant entrance of new water OR the system has been drained over and
over I am not sure that I can see how sufficient scale would get in
the heat exchanger. There will only be a finite amount of Calcium etc
in the water and even if the water is saturated the unless water
leaves the system an equilibrium will soo establish...won't it?

The build up reduces the water flow and volume with in the boiler
which will cause the water to boil thus producing the Kettling/banging. Some
time just reducing the water temperature or speeding up the pump will stop
the Kettling temporarily but if it is due to the furring up of the boiler
the only cure may be to replace the boiler.

Another reason I am not sure about this causing my particular problem
is that it only ever happens when the heating comes on. Is there any
reason that the kettling would not happen randomly whenever the
heating comes on? I think it is more likely that the water pressure
jolt kicks off the pump.

Perhaps it's all just wishful thinking and I need a enw boiler, any
other comments?


Kettling happen due to a combination of excessive heat, lack of flow and
debris in the heat exchanger. It tend to happen on older boilers which
have had more time to build up hardened particle of crud inside the water
way.

Having checked that the pump is working. Sometimes the pump are governed
by the boiler which includes are a themostat to keep them running if the
boiler is hot. These can and do fail and cause the pump to stop when it is
needed most.

Sometimes if you have TRVs on all radiators in mild weather there can be
no flow - there 'ought' to be some provision for this but...

Kettling can be anything from mild wheezy wooshy sounds up to full scale
banging and clonking that would make you think there was a detached metal
part inside the boiler.

It is likely that your system is a fully sealed type (see FAQ below) and
open vented system whilst the water is recirculated do suffer problems
over time.

If all the basic checks fail to bring releif then the best product by far
is Fernox [30 quid-a-tube] boiler silencer gel - this is injected directly
into a radiator and IME is the only think that can make the noise
less/less harsh.

HTH

--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html