Perhaps I can answer (and others can elaborate).
You essentially have to open the lockshield valves (output) more or less depending on how close they are to the pump. So lets say you have 10 radiators. You would open the nearest one 1/10 of its full amount, the second one 2/10th, the third...
What happens if you take the top of the Thermostatic valve. I had a problem recently where a radiator was cold but when I took the top of the valve it opened the valve and the radiator started heating up. There is a (silver) nut at the bottom of the white part which you have to unscrew. Once...