Before any snidey comments yes I am thick as regards any practical things around the house.
The plumber came out as the radiator in my hall wasn't working. To get it to work he turned off all the other radiators, turned up the thermostat and bingo all was well.
However the radiator in my bedroom is now not working. I've just rung the plumber and he said he may not have turned it back on properly and told me to open up the valve further.
What valve?
The top bit (which came off in my hand so as to speak) with the screwy thing that goes into the valve I put back in and screwed it clockwise to fully turn it off, and then I unscrewed it again quite a bit and now it's okay....