Radiator central heating?

Question:I Have drayton tempus 3 heating control that controls both water and central heating for the house.The boiler is working fine but when I set the pointer to heating the radiator panels don't seem to heat up.I have turned the themostat knob towards the '+' sign as well as reverese direction expecting that the heating process would be accelarated but it didn't happen.The house has been empty for a while and hence raidiator was not used for sometime now and everything seems okay to me as far as setting as concerned..any ideas please?

Answers:
Hot water radiators need to be bled from time to time. They get air locked. Also there is a circulation pump that circulates the water, make sure it is working.