How can I fix my Chaffoteaux Calydra Green 30?

My Chaffoteaux Calydra Green 30 boiler (under 2 years old) has recently developed fault where error message "-07" appears (Manual reports this as "No circulation in primary circuit"). If I turn the power off and back on again, boiler fires up and after 2 or 3 attempts at this, boiler works as normal for a day or so. Problem then returns. Is it possible that the boiler needs bleeding and if so, how do I do it? Any suggestions would be gratefully received!