Hot water heater not heating. Diagnose and find rust and corrosion on water heater. Hot water heater should be replaced. 16 year old American 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 Navien tankless water heater with new pan and test for functionality. Recommend water leak protection device (FloodStop) to prevent future damage from water leaks.