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 one with the easy-to-grip knob on where the water pipe enters the radiator. The other knob (at the other end) is for balancing purposes and shouldn't be touched.
>>>The pipe at the left hand side is hot but the right hand side is not
Well it's the hot water that you want to get into the radiator, so it must be the valve on the left which is currently stopping it (and needs to be opened).
The temperature adjustment valve is trditionally on the input (hot) end of the radiator. The lockshield valve is on the output (cold) end. Turn the valve on the hot end antti-clockwise.