Most of the water heaters that we deal with end up getting replaced. Most tanks don’t last much more than 12 years, especially in newer areas with higher water pressure.
In the past, most common repair on a water heater was replacing the thermocouple. Most water heaters today don’t even have a thermocouple, they have a thermopile. While water heaters continue to become safer and more efficient, reliability hasn’t necessarily improved.
One of the biggest obstacles in water heater repair is just getting your hands on the part. Box store units such as Kenmore, GE, Whirlpool, and Rheem will require a few days for parts to be shipped. Bradford White, AO Smith, & State Select water heater parts are stocked at all times.