Our sump pump will not shut off, however, it will not expel the water either. It just consistently runs. I have checked the outside pipe and there is nothing blocking the exit. We have not scooped out the water yet, but we know we should. We don't know what to look for though once the water is gone. We have simply unplugged the unit for now. It ran for over an hour yesterday without turning itself off once it expelled the water. This is the first time this has happened. What could be the problem?