Redecorate the wall, clean up those radiator valves with metal polish ( or even respray them with a chrome spray) and then at a later date (summer?) employ somebody who'll have the right tools and who knows what they are doing. It's a relatively small job that shouldn't cost too much in labour and you've already wasted hours posting here already. As very practical folks that are used to problem solving we get a sense of a persons ability and it would be fair to say given your posts and the responses given that no-one else has a great deal of confidence in your ability either. Please take heed of the advice given and get someone in if you insist on renewing those radiator valves, if you get yourself into trouble what we fear most is your ability to get yourself out of it.
I appreciate your concern and for now I am going to fix the wall and pop the radiator back on, hopefully without leaks (having disturbed other joins along the chain).
However I would like to teach myself some plumbing and that is why I'm here.
You claim I'm wasting my time writing but it's only because you aren't giving me any information. You are essentially creating a self fore-filling prophecy.
Perhaps the best way for me to not waste my time and for you to not waste yours in turn, would be to help teach me how not to, get into a bad situation.
So for example, you could tell me, drain the system first, that will stop flooding.
Putting a hose on a drain valve that is controlled prior to its fitting by the valve on a radiator and at worse shutting off the mains riser and if that doesn't work, having the mains in the road ready to be switched off, is a sensible approach to not flooding my house.
I mean how many more things in a chain have to go wrong before even a pro plumber will be panicking? I mean all of them would have to simultaneously have to go wrong, including the street valve malfunctioning. I think that's highly unlikely.
If I get to the point where I cannot turn off the mains in the road, then what would a plumber do anyway, apart from have insurance, which I already have.
It's not like Im trying to take off the mains riser tap here or install new valves in my airing cupboard. Im simply trying to take off a radiator and change the valves.
Im good at picking up information, Im careful in what I do and I watch hours of youtube videos and read tons of stuff before doing so. If I think something is too risky, I wont do it.
Everyone else here is being pretty damn helpful and have already given me due warning and probably sage advice on getting a pro as part of their input.
If you still think I'm missing anything then with respect, please help me by telling me.
Regards.