Diagnostic of existing water heater. The only option here was to replace. Once a water heater starts leaking from the tank, no conscientious plumber will try and repair it. They'd just be wasting their customers' money. Fortunately this leak was caught before it became a major problem. When the steel tank inside a water heater fails completely, all the water inside comes rushing out and it keeps running until someone shuts off the valve. That's why it's a good idea to take your plumber's advice when they tell you it's time to replace.