Draining a Central Heating System

Hi All,
I'm putting in central heating (for the first time) in a flat and I am thinking about what to do to enable me to drain it if ever the need arrises.
In other flats I have seen this accomplished by running a pipe through an outside wall much like a cistern overflow.
However as I'm on the top floor if I take this approach I don't think it will be possible for me to put the pipe at the required height (i.e. below floor level) and then be able to reach it outside in order to seal round the exit hole properly.
However someone in the past has gone to the trouble of doing this with a cistern overflow, and what I am wondering is whether I can tap into this for my heating drainage?
i.e. make a connection from the cistern overflow pipe to the central heating loop via a gate valve.
Any issues with this? I think the overflow inlet in the cistern is higher than my rads so I don't envisage the inlet turning into a geyser when I open the valve. Also presuambly the water will take the easier route out the end of the overflow pipe anyway. Is this reasonable to assume?
Also any probs with the building regs?
If there is a better way (or standard way) of providing a drain point please let me know.
Thanks for you advice.
Stephen
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Central heating water - with anti-corrosion chemicals and/or dissolved iron sludge in it - is not very nice stuff to be dumping at a great height, if you have no control over where it goes. It's not like clean water overflowing from a cistern!
Far better to put an internal drain point at the lowest point of the system, to which you can attach a hose to collect the water in bowls and buckets. If - as it should - it *does* have inhibitor in it, you may wish to put it back into the system rather than throwing it away, anyway.
Roger
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On Mon, 24 Nov 2003 11:06:27 +0000, Roger Mills wrote:

If you have a wooden floor with boards and joists then maybe you can route the drain point(s) through the riser of the top stair leading into the flat. If the lowest point is the visible pipework then an internal drain point will have to do (use the heavy type with O ring seals).
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Ed Sirett - Property maintainer and registered gas fitter.
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Apart from the other objections, a gate valve would be totally unsuitable. Gate valves do not close fully, but drip constantly.
Christian.
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Thanks all for your advice.
I'm using hep20 pipe and I have bought a drain cock that goes with their system. Does this avoid the problems with the gate valve and is it as good as "the heavy type with O ring seals"? It also doesn't seem to be an inline fitting as I imagined - its a Y shape with one inlet, an outlet and a shut off screw. I take it then I just form a T branch somewhere and fit this at the end of it?
I'm a bit of a novice at this plumbing lark (if you hadn't guessed!) and appreciate you guidance.
Cheers, Stephen
(use the heavy type with O ring seals).

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On Tue, 25 Nov 2003 10:43:27 +0000, Ginty wrote:

I don't know. Specialist fittings in HEP tend to be expensive. Also sometimes you need to come into copper so you can put clips on and get a solid 'feel' so that the drain plug work without having to hold it with pliers at the same time.

Yss.
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