How to stop water coming through a thermostat radiator

[Scott1989]

I’ve just bought a type 22 to replace my old single radiator.
I’m stuck on the thermostat end of the pipe work. I need to stop the water coming through so that I can replace the old with new. I’ve read different things but I’m still confused on what to do with the thermostat dial as I don’t want to take it off and have the water flow out but also don’t really want to drain the whole system just to replace one radiator.
Any guidance available please!

 

[ShaunCorbs]

You will have to drain down as you will need to adjust the pipe work coming out of the wall as most likely the pipe centres will be further off the wall than existing

 

[Scott1989]

Thank you for the reply. I have noticed the distance difference although the brackets look like they’ll allow me to correct this distance thankfully.
I can not seem to find where the main shut off is either.