No sorry you will have to drain down, if the radiator is upstairs then obviously you only need to drain it partially.
Please remember to put inhibitor in when you refill the system. Even more important if under warranty as the manafactures could refuse the warranty if there is no inhibitor. Best regards Brian
Hi, I understand you have emptied the radiator, you will still need to drain or partially drain the central heating system to remove the valves there will be no other facility to isolate the water. To partially drain the central heating system allow water out of the system and just keep opening the old radiator valve a little with a cloth under it until no water comes out. then turn off the drain cock on the central heating system.
you dont have to partially drain it just means its easier to fill.
In theory yes but I would just use a litre of inexpensive inhibitor. Or if it wont be to long before you change the other one then wait. http://www.toolstation.com/shop/p94504?utm_source=feed&utm_medium=googleshopping&utm_campaign=googleshopping&mkwid=n7cDud9q&pcrid=26799591983&gclid=CIXvyf-WlbsCFZGWtAodSy0AAQ Or Similar
Depending on the type of boiler you have will determine if you need to isolate the water supply. if you have a system boiler or combi boiler they are sealed so there is no open water supply to them. if you have a small header tank then yes you will need to turn of the supply to this. The boiler will need to be switched off. Refilling the boiler is either by way of a filling loop normally located near on on the boiler. If its a combi or system boiler. Or by allowing the header tank to fill. Obviously you will need to bleed the radiators and any air vents before firing the boiler back up.
You have a system boiler with an un-vented cylinder. by the sound of it. If your not confident in the plumbing side then yes get someone in. its sometimes quicker in the end and should not be very expensive. I have just today fitted a towel radiator exactly the same job as you are attempting, it took 2.5 hours with having to alter the pipework. So to connect a couple of valves should not be longer than an hour all going well.
Pipe freezing is a risky thing especially if the new valve does not fit easily or you have a problem, the Ice plug melts and it all gets messy. It also costs more than a bottle of inhibitor. What your attempting is not hard if you want to try it yourself. Drain it down fill it up bleed it and done usually.