Noises in unvented system

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16 Jul 2008
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Location
Hampshire
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United Kingdom
We had a unvented central heating system installed 6 months ago as part of a lot conversion. Works very well. However.....

There are some noises in the system which the plumber seems unable to get rid of.

There is a short 2-4 second vibration in the pipes around the main valve which connects the cold mains, expansion vessel, balanced mains, and hot water tank. This noise always occurs when hot water is drawn off first thing in the morning. It also happens on odd occasions through the day seemingly when hot water hasn't been drawn for a while. In addition, there is a separate noise which sounds like air in the system in the area of the valve (but may not be) when cold water is drawn first thing in the morning. The two noises are different as the drawing of cold water doesn't seem to cause the pipes to vibrate but just makes a noise.

I have secured the pipework around the valve to the wall but this doesn't stop it. The plumber has fitted a pressure reducing valve downstairs but this doesn't seem to have solved the problem (the valve and hot water tank is in the loft). There is a long 22mm plastic pipe joining the downstairs mains supply (via a water softener) to the loft hot water tank. The plumber was concerned that this might be the issue and has secured it at the top and bottom but can't get access to secure it in the drop. It was installed in an existing void containing pipes by pushing the pipes vertically down from the roof to the ground floor.

The other strange fact is that after returning from a 2 week holiday there was a rush of water going up the mains pipe for a few seconds to upstairs when I turned the supply back on. I had isolated the upstairs water supply by isolating the water softener downstairs. There was then some air in the system which was released through taps. Strangely after this the vibration noise, when hot water is drawn, didn't occur for a few days but then returned. I have not been able to find any sign of any leaks in the system and there never appears to be any water coming from the safety outlet through the tundish. Not sure if the above can be explained by a dripping tap or evaporation over a 2.5 week period.

I've wondered if the issue is with the expansion vessel. The plumber hasn't checked this but doesn't seem to think its a problem.

I may have used incorrect terminology in the above as I'm not a plumber! Apologies if this is the case.

The plumber seems to be struggling to resolve the issues and is likely to lose interest soon as we have no financial leverage.

I was wondering if anyone has any suggestions?
 
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