Radiator water flow noise - Can anyone help, please?!

[Martin1099]

Hi, Since having some house renovations 2 years ago, which included adding two extra rads, replacing others and re-plumbing the boiler , I have suffered from quite loud, (but variable) 'water flowing' hissing noise, which is especially noticable from the first two rads on the system (which happen to be thin tall vertical types (Milano Alpha doubles), see below).

The noise is loud enough to be distracting over a TV and - short of posting a clip - I can describe it as the sound of water constantly rushing thorugh a pipe!

For several years I've tried all sorts of advice from plumbers and even the rad manufacturers, but to no avail and am my wits end!

The boiler is a Greenstar 30CDi condensing type. Things we have tried include:

• Checking the valves are all fitted the right way round. The arrows show they are bi-directional
• Bleeding all the rads, in various orders, including banging the outside of them to get any trapped air out. I'm pretty confident there isn't any as water runs freely from the bleed valves.
• Taking TRVs off and pumping the pins up and down. We use E-TRVs usually, but the noise is the same whether they are fully open or mostly closed, with or without the TRV heads on.
• Adjusting the lockshields. Yes, we had trouble balancing the sytem at first, but a plumber helped do this so the new rads all get hot. this didn't seem to make much difference (maybe a little) to the noise
• We have one rad on the system fully open
• The pressure in the system has suffered from drops over time, which suggested a leak and likely air noise, but this was traced to the internal expansion vessel needing to be pumped up; in the 3 weeks since this was done, the pressure has been reasonably stable at 1.4-1.5 bar (indicated on front of boiler).

I'm not very technical about plumbing, so have really run out of things to try! Would welcome any thoughts... on my mind are:

1. when the boiler was re-plumbed, a lot of pipe bends were added on the CH flow which now has about 5x90 degree and 2x180 degree bends in the first metre or so of pipe. Could this degree of bending be somehow leading to greater noise on the first rads? (see pics below)
2. Inhibitor was added to the system after installing; someone recently suggested I could try a 'noise reducing additive' Could this be a solution; I don't really understand how this might work.
3. Would replacing the thin designer rads with more traditional ('rounder') rads potentially solve? They were expensive and would involve draining down, so only really considering this as a last resort.

Hugely grateful of any advice to avoid another year of noise! Many thanks in-advance, Martin.

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[SJB060685]

Have you fiddled with pump settings? The sounds you're experiencing can be down the pump on too high a setting. Any velocity over 1.0 metres a second is known to cause this sound, also the velocity will increase the smaller the pipework used.

 

[DaveB]

Don't quite understand why someone has left their trombone in your airing cupboard !!!!

 

[SJB060685]

It's a mess Dave lol

 

[DuncanM]

Crank the lock shield clockwise to close problem roads down a little decreasing flow of water through them.

 

[Martin1099]

Crank the lock shield clockwise to close problem roads down a little decreasing flow of water through them.

Many thanks for the suggestion... The lockshields on these rads were quite open (perhaps 80-100%), which was done when we balanced the system. I'll try what you suggest and have closed them much more and I'll see what difference that has to the noise level, whilst monitoring the heating up of the rads.
[automerge]1575810879[/automerge]

Don't quite understand why someone has left their trombone in your airing cupboard !!!!

Yes, it is quite a job! it seemed necessary to the plumber at the time. what i'm wondering is whether the water flowing around this many bends could be related to the noise. perhaps like when air flows over a wing it speeds up & you get noise. Any thoughts on this?
[automerge]1575811106[/automerge]

Have you fiddled with pump settings? The sounds you're experiencing can be down the pump on too high a setting. Any velocity over 1.0 metres a second is known to cause this sound, also the velocity will increase the smaller the pipework used.

many thanks for the suggestion. Yes I have previously tried the 'proportional low' speed selection versus the 'proportional high', but seemed to make little difference.

I've just seen that there's also a 'Max Pump Step' setting, which i've set to the lowest setting to see if this makes a difference. I'm sure there's something related to the E-TRVs that we've added since they result in just small parts of the system being on at any time, which is certainly when the noise is loudest. Will let you know if this has an effect.