How to remove a radiator?

I want to remove a radiator temporarily to allow me to decorate the room. I have done this many times in the past without any problem but recently we had a new gas boiler installed and as part of that job, new valves were fitted to all the radiators. At one end, there is the standard thermostatic valve and I know that I should turn that to zero. However, at the other end, previously we had a valve that you turned in one direction to open and the other direction to close - simple! The new valves that have been fitted are, however, different. Instead of a dial that I can turn to off there is a white plastic cover over the valve, which is fitted on by a screw at the top. I am a bit wary about loosening this screw in case that's not what you are meant to do so any advice on how to remove a radiator with this type of valve would be much appreciated.