Disassemble the venturi. There's a small elbow that feeds air into the venturi - this can get calcified and not allow air through. If you had the water level too high and it sucked a lot of water into the venturi, this happens and clogs the air intake. You might be able to force a small amount of air through, but the force of the venturi isn't enough to suck air through.
I've had this happen on my old 9002 a bunch of times. Here's what the part looks like, and what the calcification can look like:
Soak it in vinegar for an hour and it should be good as new.
EDIT: I just reread the post about backflow - do you have the venturi assembled backwards?