wrote in message
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On 2 Oct, 18:28, asalcedo wrote:
I need to add a couple of tees to a sealed central heating system.

It is a large one with more than 400 litres of water in it.

I am thinking of leaving some large radiators full of water by closing
both valves in each of them and drain the rest of the system. Then cut
the pipes and solder.

By leaving some radiators full of water I save time (shorter draining,
less venting etc.), water and inhibitor.

Can this be done or will I run the risk of unexpected water ruining the
soldering?

--
asalcedo

I did this a little while ago by freezing the pipes. I looked at the
kit you can buy from B&Q and when I had recovered from the shock of
seeing the price I had a think and wondered if you could do the same
thing with butane. I ended up buying a few tins of butane for 60p each
from a cheap shop and then wrapping the pipe in old socks, making a
pipe from a length of thin copper tube and injecting the butane into
the sock. I have a temperature probe, bought for cooking, and within a
minute or two the temperature was -15C. I know it is obvious, but I
suppose I ought to say it, if you try this makes sure it is well
ventilated and no naked flames etc. etc. It got so bloody cold that I
reckon it would have stayed frozen for a couple of hours, especially
if it was wrapped in silver foil.

You can probably get cold enough by mixing salt and crushed ice.. its
cheaper than butane and probably safer.
You need at least as much ice as the quantity of water you need to freeze so
don't think a couple of ice cube trays is enough.