Re: Radiator Valves - Replacement not so Easy!
All good advice, but I would suggest having two compression stop ends on standby.... as sometimes changing rad valves can be a nightmare.
The new valves different dimensions, might require pipe alteration...shortening is not the problem, lengthening can be if there is not sufficient play.
Just a fraction off can result in leak ( drip )
Removing the cone can be a pig, especially if it were over tightened... But sometimes you can leave the cone and nut if it fits the new valve
If there is no stop tap or gate valve, just tie up the ball valve arm in the small header tank with string to a piece of wood spanning the tank.
Draining down the system is best, prevents panic
Now if problems, from damage to pipe or what ever occurs... you can just cut back the pipe and fit the stop end(s) refill the system and have a re-think of other ways to do this.