removing vent valve or draining CH system

Hello,
I've got a very noisy boiler. Before I can afford to replace it, I'm trying to put some stuff in it that might make it less noisy.
The instructions include removing the vent valve to pump the chemical into a radiator. The picture shows the valve with a square bit in the middle and a hexaginal bit around that which I thought I'd put a spanner or socket on. But my vent valve doesn't have one. Do I need a tool for that central square bit or something?
There's a picture from the instructions here -
http://myweb.tiscali.co.uk/pgsmithson/valve.jpg
The other option (which is looking easier now) is to drain a bit from the whole system and put it in the tank in the loft. I've found the drain point behind a panel outside the house. There are two pipes there - which one do I use? Why are there two?
Thanks for any help.
Peter
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http://www.beluga.freeserve.co.uk

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In an earlier contribution to this discussion,

Some radiators have a removeable bleed assembly - with a housing and central bleed screw, like the one in the picture. If yours are like this, you can unscrew the whole thing and reveal a decent sized hole (probably 1/2" BSP) into which to pour your evil brew. Other radiators have the housing bit integral with the rad itself - so that the only bit you can remove is the central bleed screw - for which you need a normal bleeding (sic) key. This only leaves a very small hole - probably too small to get anything into.

Well, I could say "use the one on the left" - or then again, it may be "the one on the right"! I'm not sure how you expect anyone to second guess what these two pipes are - you'll need to provide a bit more information!
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Set Square
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says...

I thought there might be some standard like the pedals in a car - bit optomistic I suppose! What more information could I provide? I've got a conventional boiler in a semi detatched house. The hot water is gravity fed.
Thanks.
Peter
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In an earlier contribution to this discussion,

Are you sure that both pipes connect to the central heating? If they do - and I can't really work out why there *would* be two - it probably doesn't matter which you use.
However, one pipe may be for an entirely different purpose - such as draining the domestic hot water system for example. Unless you can trace the pipes, and find out what they connect to, there's no real way of knowing. The only other way to find out it is tie off the ball valves on both header tanks and open each drain in turn and observe: * whether the level in either tank goes down * whether what comes out looks like sludgy CH water or clear fresh water
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Set Square
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says...

Thanks for the reply - and Pete's. I'll see what happens when I open one of them. The CH water is pretty much black so I'll know if it's the correct one or not.
Cheers
Peter
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On Sun, 8 Feb 2004 21:09:18 -0000, Peter Smithson

If that's the case, then it would be a good idea to do something about it before the radiators corrode expensively away.
.andy
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> > > Hello,
> >sic
> > The other option (which is looking easier now) is to drain a bit from > > the whole system and put it in the tank in the loft. I've found the > > drain point behind a panel outside the house. There are two pipes > > there - which one do I use? Why are there two? > > > Well, I could say "use the one on the left" - or then again, it may be "the > one on the right"! I'm not sure how you expect anyone to second guess what > these two pipes are - you'll need to provide a bit more information! > -- > Cheers, > Set Square > One pipe will presumably be the flow and the other the return. If you can tell which is which I suggest you use the return drain but either or both will do. I had a similar scenario where I needed to put Fernox inhibitor in the system. I did it twice once using the radiator and once using the header tank. The header tank method was much simpler. Switch off system and shut off header tank flow( if no tap - tie up the ball cock) Undo drain(s) - the slower, within reason, that you do the draining the better as the water in the lower radiators could be undisturbed. Time the empying of the header tank - say 15 mins - carry on for say 5 mins more to ensure that there is plenty of capacity in the circuit. Close drain and introduce "stuff" down header tank output pipe.(plastic hose could help on this) Switch on water - switch on system and bleed as necessary. Pray for quieter boiler !!
Pete Stockdale www.thecanalshop.com
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