Hot water heater not heating. Diagnose and find rust and corrosion on water heater. Hot water heater should be replaced. 18 year old American Standard water heater. Recommend replacement Rheem tank water heater, or Navien tankless water heater. Average water heater life span is 8-12 years old. Install new Rheem tank water heater with new pan and test for functionality. Recommend Gemline water softener to protect new water heater from hard water damage.