I would anticipate that the overflow valve is stuck open. If not, it is definitely broken and needs to be replaced. Believe it or not, this is not at art. As long as the drain line is screwed to the valve and pair of channel locks will remove it. After that, take a pipe wrench and remove the valve. It is a very cheap fix. Make sure to use pipe dope when reattaching. Be gentle but firm when loosening and tightening. You don't want to damage the water heater. Good luck!
________________
I think I am a
handyman, but don't ask my wife!