Blinking?

[Jameson]

I have a Whirlpool 50 gal. water heater with the energy saver system (circuit board controls). I've used it for four years and yesterday we ran out of hot water. It's showing 1 blinking light, which, according to the troubleshooting chart, indicates the tank isn't filled with water. But I'm getting good water flow from all the hot water spigots in the house. I've pushed the reset button several times but it just won't work. Is it possible to have an air lock in the tank, even though I have good water flow? Or might I just have another bad board (this is the second board on this unit)?
Thanks.

[Otahyoni]

Could there be a bad water level sensor?

I don't know anything about them, just an idea...