Hi
currently have the same problem with my eber hydronic d5, although not blue smoke but white smoke. Blue smoke sounds odd as thats usually the exhaust produced through the burning of oil for example in an engine. white smoke is often due to incomplete combustion and black smoke for over load.
saying that i'm not sure why these units seem notorious for producing excessive exhaust smoke and hope to have mine serviced next week. one thing i wonder is that i fitted a silencer last month which has a drain hole in the bottom for condensation, and hence blows a steady stream of exhaust into the engine bay. Maybe this is entering the unit and effecting the combustion.
andy