If the screen is not dirty, and the flapper valve to the turbine inlet is open, then the problem is mostly a stuck turbine impeller. The turbine impeller on my F7431-900 has seized TWICE!! The shaft for the turbine is not made of stainless steel, therefore is subject to corrosion. If you have a handy husband or boyfriend, give it to them, because some disassembly is required to access the turbine unit. After the turbine is removed and opened up, get some P'Blaster and squirt is on the shaft. P'Blaster is a rust removing solvent and is great for freeing up rusty nuts and bolts. Allow the P'Blaster 20-30 minutes to penetrate the corroded shaft. Then, grab the impeller and wiggle it back and forth, until free rotation is achieve. The last time my brushes stopped rotating, and I disassembled the turbine, it was really siezed up. I thought I was going to need to buy a new impeller assembly. But, that P'Blaster is really great stuff for breaking up corroded parts (it's like WD-40 on steroids!). I did need to give the turbine's impeller a good twist to free it up. If you can't get the turbine impeller to rotate, then buy a new one (about $27.00). Then, you can just install it and save a bundle on labor. I think I want to become a Hoover vacuum repairman. Their business must be booming because Hoover is putting out a poorly designed turbine unit. Boo, Hiss...... shame on Hoover for selling us **** like this.
PS You can get P'Blaster at any auto store, like Pep Boys, Autozone, etc.