Hello: I’d like to know how the elements fail. That info could give guidance as to what to do next. Also, it would be useful to know what voltage you’re getting and if it fluctuates much. Do lights ever vary in brightness? Are you on a well? Air could be a problem if you are. What is the water quality? What kind of heater is it… a glass lined steel tank or plastic?
I know cars are sometimes lemons, but with water heaters, well, some are simply misunderstood 😀
Anyway, more info about the circumstances around the heater would help.