In the manual it says no pressure rise was detected on turning on the pump - water pressure sensor and or pump defective, air in heating system, quick bleeder defective, too little water in appliance, check adjustable by-pass, connect external expension vessel to return.
Ensure you have at least 1 bar pressure in system via guage or button, if not add some water via the linked water tap and pipe. Also bleed your radiators to ensure no air in system.
hope helps
helpful, January 2010
