How can I get veirfy my radiators are operating properly?

MY Worcestero Bosch high flow 400 had not been working for the past month. Recently the Heat exchanger and pump were replaced along with other minor components. The system appeared to work but was slow to heat the radiators. (Hot water works well, finally). When the pump is operating it sound like a washing machine; like there may be air in the system; I venter all the radiators in the flat, but it doesn't appear to have any affect.