Below the boiler you will find a valve gauge reading 0-5, most likely, your's will be sitting at 1. You need to refill the pressure for the boiler by turning the black and blue levers nearby. First unlock the black pressure lever, then unlock the blue. Depending on which ones are already open/closed, you will hear the pressure slowly building. Fill this to around 2 or 2.5 on the gauge. Turn the levers off in reverse order to stop the pressure from building.
Steve, September 2010