I vote check valve also. If you leave the hot off for a few minutes, when you first turn it on do you get a little bit of water then nothing? This is what I had last year when my check valve broke. The valve is basically a flat surface with a stem coming out the bottom. Think of an intake/exhaust valve on a gas engine. There is a spring on the stem and a clip that hold the spring in place. The spring holds the valve closed so water can not feed back into the out port of the water heater. On mine the clip came off, allowing the valve to flow with the water. About 1 inch until it hit the elbow where the hot out line screws to the water heater. At that point it became a plug. Preventing water from flowing out of the water heater.
Temp fix is to turn of water heater, turn off water, and drain water heater down to below the hot out line. At this point you can take off the hot out line and remove the piece that is stopping things up. Put it back together, fill water heater and return to normal use until you can get the valve replaced.