Working on my Hayward pump. Came home a couple of days ago and the pump wasn't working - just humming. Today I removed the pump from the wet end and fired it up and it works just fine. Put it back and it doesn't. Does this mean that the impeller is broken? I didn't really want to take it off until I'm sure, but from the posts I've read that sounds like the culprit. Am I on the right track here?