On Mon, 29 Mar 2004 03:37:20 +0100, John Rumm
wrote:

Blonks wrote:

The only problem we have had until recently was the boiler cutting out
due to air in the system (a few years back) - plumber found the vent
pipe wan't venting due to an air seperation thingy problem. He didn't
replace this but did something that involved cutting the feed pipe to
it and all was fine.

It sounds like someone may have placed the expansion pipe (i.e. the one
that runs from the main heating circuit to over the top of the header
tank), too close to the "suction" side of the pump. This can cause gobs
of air to be drawn into the system as the pump starts up. The cure is to
move the pipe to the other side of the pump (or combine it with the feed
pipe from the header tank).


The pipes have been this way since day-one, so probably not

Recently there have been banging noises from the pipes/ boiler - it
wakes us up in the morning.

Could be one of several things, scale in the boiler causing "kettling",
you could have lots of air or gas in the system. The pump could be
failing - hence giving a lower flow rate, this is also likely to cause
kettling as the water will get hotter with each pass though the boiler.
A failing pump can also introduce vibration of its own.


I think there is mild kettling ,but I think an air lokc osunds the
most likely - probably due to a gunged up air separator?

If the system has spent much time running without inhibitor any of the
above are quite likely to occur. Also since air in the system acelerates
corrosian, and corrosian produces gas... you have a degenerating situation.

the plumber came and did a boiler service and injected some furnox
boiler silencer to the bathroom rad. This was fine for a week then
the noise came back. I had a look in the feed/expansion tank and saw
rusty gunk on the surface of the water - I assume this is what the
furnox does ?

No this is what corrosion does ;-)

I bialed this out and drained the system using all 3 drains on the
rads. This again fixed the noise for a week and it then came back.

Sounds like air/gas in the system could be the cause then.

It only seems to be for the first 5 mins of the boiler heating up.
After that it is still there when boiler switches off/ on - but not as
loud.

Also could be air - as it circulates it will disperse through the water
reducing the effect. After pump stops and the water cools the air will
begin to separate out and accumulate somewhere in the system ready to be
swept off again next time it starts up.


That sounds good to me. I've got a real plumber coming around next
week to have a look.
I then got some sentinel x100 + x200 and partially drained the system
and added via the tank.

It hasn't worked and the noise is getting worseand I'm £25 worse off !

So, my question (eventually!). Why has the noise gone then come
back? Is this somehow related to the initial problem with the vent
pipe / air separator ?

I would guess this is the cause...

could there be some rust/gunk in the system cuasing it ? Is there some air in there causing/adding to the problem
- should I have done any draining/bleeding at the boiler?

The fact that you have had an airlock in the past suggests that there
may be some of you pipe work that is routed in such a was as it collects
any air circulating (normally you would expect the air to accumulate in
a radiator when it could be bled out).

Would it have fixed it if I had fully drained the system then added
the chemicals?

Not if you still have a problem with air being draw into the system via
the expansion pipe for example. (a blocked feed from the header tank can
also cause similar problems).


Many thanks for the advice

Ian
--

What we have here is a failure to communicate.