A residential storage-type water heater probably requires less attention than any other home appliance.
Problems are usually few and far between.
But I know from experience that when a problem occurs, it can be elusive, annoying, and nearly drive you mad trying to figure out a solution. The water heater in question was under a warranty, but the warranty was only against a leaking tank. Since it had been first installed we had experienced an erratic hot-water supply. In addition, the tank was smaller than the old one, again for the sake of energy conservation. On those occasions when we would run low on hot water, I would alternately blame it on the fact that we had an early version of the energy-efficient models and the bugs weren't all ironed out.