Do you mean cistern or cylinder, sistern is a tank usually in the loft so highest point so doubt the air bubbles are hear. Have you tried back filling? Different ways of doing this but basically you want to push mains pressure up the hot water pipes to shift bubbles.
This can be done if you have a mono block tap, hold you hand over the end and open both hot and cold, because you are blocking the tap the mains will force it's way up the hot as it has a higher pressure. Leave for a while then leave the hot running. Not sure why you were advised to turn of water to cistern, this will create more air
