How old is it? I hear they only have about a 10 to 20 year lifecycle, and they are rarely repairable, unless it's an obvious problem with a fitting. Some people replace them before they go bad at a specific age, because when the go bad it can be a disaster. I don't know what that age is though. Mine's probably at about that age, since my house is 15 years old and so is the water heater.