My water boiler is leaking alot of water. Also it's making a hissing sound like their is a hole or something?

Also when I turn off the water supply the hissing sound stops. But the pilot of the boiler still turns on and water gets hot. however the pilot goes out when the basement gets flooded with water cause by the leak from the boiler. Any suggestions on how to fix the issues or what could be the problem. Or should I replace the boiler, the boiler is only 1 and half years old. Thanks