I've done the "self-test" which shows it's working fine. Left it completely unplugged from the unit and power supply overnight. Opened and checked impeller is clear and moves freely when doing self-test. I'm out of warranty. Power unit seems fine, too. Can anyone help me troubleshoot without an expensive diagnostic and repair bill? Our last problem was the power cord, which was only discovered after Maytronics made us ship the entire thing to a repair center (shipping both ways was at expense though it was under warranty).