Draining GCH System

I need advice on the difficulty of the following:
I need to replace a radiator valve in the upstairs bedroom. My GCH system has a combi boiler, fed off the water mains directly.
So far, I understand I need to do the following:
1-Shut down the boiler & let it cool off 2-Shut the water mains 3-Drain the system at the draining valve downstairs 4-Change the valve on the upstairs radiator 5-Refill the system 6-Bleed the air out the radiators 7-That's it!
So! Here are the questions:
-Did I forget anything in the above steps? -If I drain the system, I also drain/introduce air in the boiler. Is this not a problem for the boiler? Will all the air be flushed out when I bleed the radiators? -When I refill the system, do I need to mix some anti-corrosion fluid of some description with the water? If so, how do I do that considering my system is fed off the mains.
Thanks for your help !
GM
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You don't need to shut down the water mains. There shouldn't be a permanent connection between your sealed pressurised primary circuit and the mains supply.
There should be a braided hose connecting the mains to the system. This should normally be physically disconnected (but frequently is not) and the valves shut off. When refilling, you attach the hose and open the valve. When finished, you ensure that all valves are off and the hose is disconnected.
When refilling, ensure the automatic bleed valve is on, if it has have one.
It is easist to refill with two people. One sits by the filling loop topping up when the pressure goes down. One goes round opening the radiator bleed valves. With only one, it takes longer because you need to keep going back to refill.

The majority of the air will come out through the automatic bleed valve and when bleeding radiators. There is also a substantial amount of air entrained in fresh mains water. You should, therefore, keep the automatic bleed valve open for a while and rebleed the radiators a week later after this air has come out of solution. Also, bleed manually if the system sounds funny, with clanking and other unusual sounds.

You MUST install inhibitor, such as Sentinel X100. To introduce corrosion inhibitor into a sealed system, there are many solutions. You can prefill a radiator with it before reconnecting it, you can get syringes for squirting it into a bleed valve. Best of all, when the system is drained down, install an additive filler point, which is just a short vertical stub in pipe, preferably near the top of the system, with an isolation valve in the middle. You just open the valve, insert a funnel and pour the chemical. You don't need to buy expensive proprietary solutions, but don't forget to close the valve before refilling!
Christian.
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I installed an additive filler point when I fitted my new gas boiler - very nice it looks too.
6 Inches of vertical pipe at the very top of the system. I did not bother with an isolation valve. Instead I just used one of those plastic end cap fittings - like the plastic pipe joints but closed at one end. I just DEPRESSURISE THE SYSTEM FIRST!!! Then pop the cap off. Drop in some X100 using a funnel, and put the cap back again.
Geoff
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Thank you Gentlemen, I shall have a go at it this week-end!
GM
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Well, I am pleased to report that I now have good heating in all my radiators! I followed your instructions to the letter. Everything went nice and smooth, My system is now back online, with X100 added and all.
Thanks a million for your help!
GM
snipped-for-privacy@yahoo.co.uk (grandmainger) wrote in message

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Yes, I can see that it could cause problems if you forget to drain the system down first! Perhaps an isolation valve is still a good idea? They cost about 80p, probably less than a push fit stop end.
Christian.
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80p - where???
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Looks like I've been paying too much. Screwfix do them for 49p.
http://www.screwfix.com/app/sfd/cat/pro.jsp?ts 425&id483
Christian.
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Hmmm. Very good :) I'm sure that I've paid Screwfix more than that. Are their catalogue prices different from the web-site?
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On Wed, 15 Oct 2003 16:36:53 +0000 (UTC), "GB"

Yes, they freely volunteered that during a phone call once. Also the content can vary between the two. The numbers for items appears to be consistent though.
It's worth checking the paper versus the screen where an item is listed in both forms, as it can produce savings on odd occasions.
Take Care, Gnube {too thick for linux}
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from what i know...when cleaning your rads with fernox you have to leave this for a period and then flush through system.With regards to the steps illustrated above they seem all in order, generally when re-filling from my experiences yet to come across air-lock. Go for it and good luck.
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