Should I be concerned about a green crust on the copper pipes on my boiler?
When copper oxidizes, it turns green.

Usually there has to be some kind of catalyst to cause oxidation. Potential catalysts include salt, iron and any kind of acid.

Acid will form in water due to dissolved carbon dioxide. Usually if copper is getting green, it is because it is getting wet. In the case of a boiler, this could be due to water in a humid environment condensing on a cold pipe.

A quick fix is to clean the pipes by rubbing with scotch brit pads, polish with a metal polishing pad (do not use metal polishing compound, just a dry pad), then rub the pipes with a 10% solution of lye. Lye is powerful stuff, so handle it with care and use rubber gloves and eye protection.