UKC

Following on from other central heating questions on the forums.
My central heating system is really noisy with a loud rushing water sound at all the radiators.
The boiler is a 4 year old baxi duotec 28kw and most of the pipework and radiators are new. The system has been flushed recently and inhibitor added but the water that was drained out was quite clean and only slightly yellow.
Anyone got any idea how to quieten things down? I thought about reducing the pump speed but apparently the pump speed is automatically determined.

In reply to gethin_allen:
I think you need to fit an automatic air vent somewhere high up in the system. You may also need to go round bleeding all the rads for a few days. Do this with the pump off.

You can reduce the pump speed, there should be a small black selector on the front of the pump with three possible settings. Generally after a refill my own system is noisy but it usually settles down after a couple of days. Your problem may be that the pump is sucking air in somewhere.

In reply to gethin_allen:

Has this always been the case? The pump should be at 3 as standard, unless it's a newer Grundfos version that sets speed automatically.
You've probably already tried but are all your lockshields fully open? How many rads do you have?

In reply to Rigid Raider:

Thanks fort he suggestions, I don't think it's air that's the problem. When I say "recently flushed" I'm talking just before christmas, but it was noisy before then.
The pump is built into the boiler and there are no switches or dials on it.
The boiler also has an auto air vent built into it.

In reply to Jonny S:

Has this always been the case?
When the boiler was initially installed I don't remember it being noisy, but I had a load of radiators changed/added later on and then I really noticed the noise.
The pump is Grundfos, it's built into the boiler and I can't see any switches on it where I had switches on the old one.
I have 7 radiators plus a small towel rail, 6 of the 7 rads are new, mostly type 21 ~1200x500 but one or two bigger.

I'm not sure about the lockshields, all except one of the rads has a TRV fitted, should all the lockshields be open fully?

In reply to gethin_allen:

Aye, pump will be at its maximum speed then. Sounds daft but were any of the new radiators downsized form originals?
Open all of the lockshields fully and see if that helps.

In reply to Jonny S:

Sounds daft but were any of the new radiators downsized form originals?

Maybe one or two just slightly in length, but the old rads were single panel and the new ones are all rated to put of much more heat than the old ones.
I'll give it a go with the lockshields tonight and see what happens.

In reply to gethin_allen:

A full vent of the system if you've not already done so may help. You may have an airlock somewhere that won't just come out by bleeding the rads. If opening all the lockshields doesn't remedy it then let us know and I can talk you through a full vent mate.

In reply to Jonny S:
Amazingly, opening up the lock shield a bit on a few rads seems to have sorted things out. This is totally counter intuitive to me as it sounded like the water was moving too quickly and previously only closing down the trv stopped the noise.
Thanks for the help

In reply to gethin_allen:

You're basically increasing the flow through the lockshield mate, glad to be of help.