is this pump toast?
 

I have a Red Sea Berlin pump I was using with a Prizm Pro. The pump will run out of the water, but as soon as it's put under water it clunks to a stop. Sometime the stop is instant, sometimes it clunks a few times. The impeller is new.

Is it dead? Any way to bring it back to life?

try rotating it a few times underwater, perhaps there is an air bubble. If that doesnt work, open it up and clean it. Also check the shaft that the impeller and magnet slide on to make sure its not broken. If you do all that and still nothing....prolly broke. lol. hope it works out for ya.

Yeah, I've checked all that stuff. Impeller is brand new, so the shaft and stuff is good. I've tried shaking all the air bubbles and stuff out of the pump before startup, all to no avail.

It just sucks, I don't want to go spend $50 on another pump, lol.

OH, check one more thing. Take a look at the impeller. Even tho it may be new there might be something broken on it. There is a little stopper somewhere on it (at least its like that on the MAG pumps) that stops the propeller from spinning backwards. It's possible that piece might be broken causing the propeller not to spin. Just a thought.

Have you cleaned the pump in a vinegar bath? Maybe there are deposits down inside where the impellor goes?

Yeah, I cleaned it.

The last impeller I had became disconnected with the magnet somehow, so the magnet spun, but the impeller didn't move - This happened sometime during the night and I found it the next morning.