Any Plumbers in the house?

[fazersharp]

I forgot to add I am trying not to drain down the whole system as I can isolate the one leaking rad.

I have an unvented system and was able to shut off both sides of all the upstairs rads and so trapping the water in them so all that I had to drain off was the 1 barr pressure and a few pipes that were higher than what I was working on, took off old valves and there was the water level sitting at the top of the pipe.
The valves i linked to have a 15mm connection at both ends and are reversable so you can fit howerver you need, but you need to know what size yours are as some are bigger