Central heating /hw system banging

Chaps hi,
hoping for a bit of advice here. I have recently moved house to a property which was built circa 1987. One item picked up on the survey was that when the bolier came on (ch or hw) it made lots of loud banging noises. So it has been doing this for at least 6 months
This didn't bother us too much but now we have started to use the CH with the onset of winter it is waking us up every morning with a *very* loud BANG. Having recently had the old analogue programmer fail (and having to update it and the thermostat myself) I have decided that it has to be worth an attempt at self diagnosis - and then possibly trying to fix it myself or get some one in.
I have looked through similar posts but was hoping that this might make sense to someone out there.
Here is all I can tell you about the system.
System type: Fully pumped, Mid Position valve system, install 1987 by builders Boiler: Thorn EMI apollo fanfare i Pump: Grundfos Selectric (TF110 IP42)??? Mid position valve: Sunvic SD2752
The rest of the kit (stat, programmer etc seems fine)
The bang happens when the heating or HW comes on, normally makes 3 or 4 bangs and then is quiet until the next time it goes off for a while. I have checked the rads and there is no significant air in the system, the noise seems centred around the cupboard where the boiler, pump, HW tank are installed. The bangs seem to travel through the pipes and it seems that one pipe has now broken the plastic clip it was in - symptom not cause though I think. The only other thing I can think to add is that in some rooms as the CH or HW comes on the radiators make a sort of rattle - like some hard sediment in them is bein disturbed by the water flow?
Any tips as to what I should look for gratefully received
Tim
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Two ideas spring to mind:
1. Air in the boiler- especially if the neither of the water pipes exits the boiler at the top and continues 'up' . (If they don't, air can get trapped in the boiler and it will stay there- in the extreme enough can collect to stop the boiler lighting.) There is (usually) a bleed valve in the boiler at the top of the heat exchanger.
2. Is the pump starting up reliably? If it 'sticks' the water in the heat exchanger could be boiling, making the 'bangs' and the shock kicks the pump to life.
--
73
Brian
G8OSN
www.g8osn.org.uk
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Brian Reay wrote:

I had the same problem a few years ago - very loud banging noises whenever the heating fired up. The British gas solution to the problem was an offer to relieve me of 2200 for a new boiler etc. My solution was to drain absolutely everything containing water, then to flush the heating system with Fernox, and then fill with Fernox inhibitor. The problem must have been an airlock somewhere in the system. I then had a worrying time when I lost the shower and all hot water, but I persevered and got it all working eventually. This was over two years ago and it's still working fine. Central heating is really somewhat of a black art and problems take time to solve. Unfortunately the professionals don't take the time - you couldn't afford it if they did. For example, a full heating system balance could take a full day - would you be prepared to pay for this? - this is why it's never done properly unless you DIY.
Terry D.
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snipped-for-privacy@hotmail.com (Tim) wrote in message

Tim,
Exactly the problem I had when we moved into our house built in about 1987 (Myson Appollo 40k btu, fully pumped Y plan, and lots of banging on startup. The banging was preceded by the boiler whistling. No sound from the pump until the banging then a very obvious hiccup and lots of circulation noises. I verified that in about 50% of the time the pump was not starting immediately that the boiler fired up, the water in the boiler heat exchanger boiled and made the explosive banging noises and the vibration in the pipes kick started the pump.
Eventually the pump failed to start completely (coldest day of last winter) and BG replaced it (I was away at the time so my wife called out BG under the service agreement which is why I have it) no further problems...just minor circulation noise. BG wanted to replace the heat exchanger or preferrably the entire boiler before I pointed out by phone that the pump was not working.
More recently I finished the job by a complete primary system flush and clean according to Andy Hall's procedure and replaced valves with TRVs. The system is now like new..even the minor circulation noises have gone.
Cheers
Ian
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Thanks guys,
I think I will try and clean out / flush the system, check the pump is starting whe it is supposed to and go from there.
I have eleven rads in the house, all of which get hot nicely but none have TRVs. I am going to install 9 trv's and leave them off the small rad in the en suite shower room (I think it might be the bypass as it comes on with HW or with CH) and the rad in the entrance hall (this is always a cold room and the room stat is installed here - I have read the trv and stat *may* interfere with eachother).
How much of a pain is the flushing? Is it worth trying to install all 9 valves in one hit when the system is empty?. Also I would like to move a downstairs radiator a foot or so in order that I can make a new internal doorway - as this means digging up the concrete do you think I should try and do it all at once?
Thanks for the help it is much appreciated and I wait for the day that someone asks a Q on here that I have the answer to ;o)
Tim
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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. 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.
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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?

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

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
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OK,
I am wondering if my motorised valve might be the problem... please see point 2 below.
Last w/e I went out and bought 2 litres of non acidic descaler, added these to the system via the header tank (perhaps my system is not sealed as per your definition Ed!) and flushed it through to make sure that the descaler got into circulation. I also gave all the rads a good bleed
The banging continued ( I am not sure how long it takes for the descaler to work but presumably a while as it will only work on contact => thick layers of deposition will take a while to go).
Couple of days ago I bit the bullet and fitted a replacement pump - got a Grundfos Alpha+ 15-50 as every one seems to think they are good here. The noise has definitely reduced. Now there is perhaps one bang (was 3/4) and no or little pipe groaning building to the bang.
However there is still a bang. Diligently I sat by the boiler at 6.30 this morning waiting for it to come on and notice two things
1) When it did come on there was one medium bang and then it sounded like the water flow through the system really took off (lots of whooshing)
2) Before the heating came on the HW circuit was energised but not running yet (HW tank stat was not calling for heat) All the pipes were cold (ie bolier had not run) BUT the valve cover and body was really hot - say 45C or so yet the water temp in the pipes was ambient. Would you expect the valve to run hot like this? can the valves fail in this way and...could the valve also be responsible for making the flow sluggish on system start up hence the banging???
Thanks again for all your response - very much appreciated
Tim
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On 5 Nov 2003 06:36:37 -0800, snipped-for-privacy@hotmail.com (Tim) wrote:

I think it depends on whether you believe in fairies and the completeness and professionalism of the construction trades.
Logically you are right, but I think the reality is not going to be that.

Then I think that you will need to drain as best as you can. A wet/dry cleaner ought to be able to pull most of the water out of the pipes in the screed if you can figure out a way to hook it up to a radiator valve union reasonably well.
Given the circumstances, it would be an idea to perhaps go for radiator valves with a drain on the pipe side or alternatively fit a drain cock below each valve. Then you can at least flush at each place.
.andy
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