Disappointing warranty service

My geyser was replaced under warranty, and then I started having issues with air in my hot water. Contacting Ariston service, they tell me it is an anode problem, but there's nothing they can do as the anode is not covered in the warranty. If they had checked the geyser was in order (in all aspects, including the anode) before coming and replacing under the warranty, I wouldn't be having this issue. Very disappointing.