What work have you had done ? have they drained or altered the system ?
If not it may just be the thermostat valve sticking shut through lack of use (quite common)
First check the lock shield valve on the left side of your radiator is fully open (anticlockwise) looking down on valve using a spanner or pliers. Also remove the thermostatic valve top at the knurled nut under the plastic head (no water will come out) and make sure that the little pin sticking out of the valve is springing up and down, If it is stuck down gently tap it straight down with an hammer to free the stuck valve below from it's seat.
If this makes no difference bleed the radiator, turn off all the other rads and hot water if possible and turn on the system to try to get the pump to push any air from the pipework into the rad.
Pete
