Hot tap bassoon!

12 Jun 2009
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United Kingdom
Have searched around trying to find the answer to this but seems plumbing noises are many and various and hard to be sure about!

We've got an oil-fired boiler and recently had the traditional hot water cylinder and cold tank replaced with one of these unvented mains pressure systems. It's a megaflo type setup (GAH Dualstream) with an 'accumulator' in the loft which as I understand it stores water at mains pressure (deemed necessary as we have a small bore mains supply pipe to the house).

Since we've had this new setup, we've been getting a loud noise sometimes when running a hot tap. The noise isn't a hammering or banging so much as a long 'bassoon' type sound that varies in pitch as it sounds. If you leave the tap on, the noise dies away after a few seconds.

It happens on every hot tap in the house, but only intermittently - i.e. at least once a day, on at least one of the taps, but most times you use the tap there's no noise. It's most likely to happen first thing in the morning.

So far it's never happened when the plumber's here, which is pretty frustrating - he's installed the system and is currently installing our new bathroom so he's here quite a bit but hasn't yet identified or fixed the problem, so it would be great if someone could point me to a likely cause!
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Dan, thanks for these suggestions, I don't think it's the taps because there's only one old tap left (in the kitchen) and the noise is definitely not coming from the tap itself - seems to be coming from nearer the cylinder.

If it's loose pipes I'd expect it to happen every time we use the taps but in fact it's only once or twice a day... very odd.
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As the pressure drops in the Accumulator the non-return valve can vibrate. Does it die away if say running a bath? I had in on my own kit at home, changed the NRV in the end.
Yes, the noise does die away after a few seconds if you keep the tap running. It only happens on the hot taps and mixers e.g. bath filler.

Definitely sounds like it's coming from somewhere in or near the cupboard with the cylinder and gubbins in it, or the accumulator (in the loft directly above). Can't be 100% certain though because the noise has normally stopped before I can track it down!!
Still haven't managed to resolve this* - and today I went to run the tap and there's a dull ping/clonk noise from the cylinder cupboard and all of a sudden the water slows to a trickle. I open the cupboard and have a look and the gauge that normally shows 3 bar is now on 1 bar. No sign of any leaks. Any ideas what might be going on?

*I had the rep from the company that sells the Dualstream stuff come and take a look, and he suggested putting the pressure vessel on sideways, which we haven't had done yet

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