Not a whole lot i can add to this. There is no hidden filter on this model that can cause issues like this. Did this problem just start all of a sudden, ir has it been there since you got it?
The pumps can be brought back to life if they are slightly worn. If the pumps are worn, your drive power would be lower than it should.
If you decide to go this way, i can give you details of what to do, it will involve removing your main pump, it's not a hard job, but you need to keep things clean clean clean.