When you bleed any water out of the system, the water pressure inside the boiler will drop. With the boiler off, open the water filling loop valve until you have a pressure of about 1 bar. When the system is running, expect a small pressure increase but when the boiler shuts down the pressure should drop again. Don't overfill the boiler though - you'll have to remove more water if you do.
John, December 2007
