i have a tunze nano skimmer that i picked up used from a friend.i dont think it is more than 4 or 5 months old. went to empty the collection cup today and noticed the pump was not running.i took the whole thing apart and cleaned pretty well.took the pump out and removed the impellor and cleaned as best i could inside.i did not take the shaft out because i was not sure if it comes out or not and did not want to break it.when i put it back together it still did not work.is there a common thing i should check?or is it likely that the pump is just out?