The RIOs can be kinda touchy. The larger Rios don't seem to have a problem, but the smaller ones do on occasion. The piece that forms the intake or the retainer for the impeller seems to bind the impeller once in a while. All you need to do is remove the pump from the tank, plug it in and loosen the retainer by aligning the slots in the retainer with the prongs of the pump and pulling it a few mm from the pump, the impeller will start spinning. while it is spinning, tighten the retainer back down and make sure the impeller is still spinning. Unplug the pump and put it back where it came from, then plug it back in. The other thing that can happen, which can happen to any submersible, is that a few specks of sand or debris got into the impeller assembly, in that case take the impeller out and flush it out real well with water, reassemble and place it back into the system. This really isn't a defect in the pump, the smaller pumps simply don't have the torque to overcome friction sometimes. It's a small price to pay for a pump that will move that much water using so little electricity.
