Radiators not working

Depending on what system you have sometimes this can be caused by an air lock. I have always found the best way of doing this to shut down the radiators that are hot by turning them off at the lockshield valves located on both sides of the radiator (where the copper enters the radiator). Once these warm rads our turned off, turn the heating on and then bleed all of the cold radiators. This should pump the water around all of the other rads by passing the two that are warm and hopefully push through any air lock. If this works and the radiators all warm then re open the all the radiators, bleed and the system should balance.