In an earlier contribution to this discussion,
Markus Splenius wrote:

On 25 Jan 2005 04:06:02 -0800, (Andy Hide)
wrote:

I need some advice on the best way to drain down my CH system to add
an additional radiator. I'm in a first floor flat and the pipes run
under the wooden floor. There is a drain cock on one of the radiators
but correct me if I'm wrong this will only drain to the level of the
drain cock? All the pipes under the floor will still be full of
water.

Does it matter if the pipes under the floor are full or water?

Er, yes!

If the water is drained below the level of the radiator, there won't
be any spillage when you disconnect it.


True, BUT the OP wants to add an additional radiator. This will normally
require extra branches off the low level flow and return pipes. Breaking
into these will cause a flood if they are still full of water.

Question to the OP: Are the pipes under the floor all joined by soldered
joints, or are there any compression joints? If there's a compression joint
you can get at, this is what I would do:
Firstly fully turn off both valves on all radiators to keep them full of
water - making a note of the open/closed position of each lockshield, so
that you can restore the balance.
Secondly, if it's a vented system, put bungs in the fill and vent pipes to
keep the water in the F&E tank
Thirdly, drain as much of the remaining water as you can, using the drain
cock which you mentioned.
Finally, crack a compression joint under the floor, with a shallow vessel**
under it to catch the remaining water.

** Foil take-away food dishes are ideal for this. You will either need 2,
and empty one into a bucket while the other is filling, or you will need to
do the joint up lightly each time you remove the dish to empty it. Also use
old towels under the dish to absorb any slight spills.
--
Cheers,
Set Square
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