I have a Dolphin Premier that has stopped moving. This happened once before and TFP experts suggested a problem w the impeller, which WAS the problem (broken) and a new impeller replacement had it working fine. It's stopped moving again, and I've inspected the impeller, and it's fine - moveable manually - but the Dolphin still isn't moving and the impeller doesn't seem to be rotating. Any ideas about what the problem might be?