has the system been vented ( the radiators ) if not vent them then top the pressure back up . you need to vent the heat exchanger which is inside the boiler at the top next to the fan and has a plastic tube connected you just unscrew the nut ONLY 1 OR 2 TURNS till the air is released then tighten back up but dont overtighten, then top the pressure up if needed the system should be ready to fire up . hope this helps
kevin
April 2008