pls help to confirm this is rads drain valve

7 Mar 2014
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United Kingdom
I need to replace rad upstairs to a smaller one hence would need to realign the pipes.
It appears there is no radiator with drain valve but there are 2 on Unistor cylinder.

This is unvented system with 2 zones - 1) underfloor heating and 2) radiators (2 downstairs and 5 upstairs).


I presume the CH drain valve is the lowest one fitted on CH return pipe - can someone please confirm this as I don't want to drain cylinder by mistake.

Also I was going to isolate downstairs rads by closing both in and out radiator valves and isolate underfloor heating circuit by closing both red and blue valves in the underfloor manifold - is this correct way of doing it ?

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OK, thanks

your picture is not showing.

As it is an unvented system, you do not need to drain it. Once you have depressurised it, you can close both radiator valves and remove the radiator (turn it upside down before carrying it away). You can then remove one radiator valve, only, and water will not run out. Make your changes, and close the new valve before you do anything at the other valve.

As long as it is an unvented system, and is depressurised, and you only have it open at one point, water will not gush out, because no air can get in to displace it. It may drip a bit, so put down a bowl and old towels.

You will not be able to solder wet pipes.
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sorry, here is new link -


Radiator has been removed already before the work on room started, both valves closed but I will have to remove pieces of pipe with old valves and add length to one pipe and shorten another one - under floor boards, adding new elbows to connect to new radiator valves. I initially was going to solder but since it may be difficult to heat pipes enough decided to use POLYPLUMB grey pushfit elobow instead.

if no need to drain - how do i depressurise the system ?
you can solder everything except where you connect your new pipes to the wet ones.
Thanks JohnD, is it ok to use pushfit then on a wet pipe?
Thanks a lot, all done without draining, - lots of time and water saved!

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