Check the impeller. Sometimes even the smallest debris in there can make it heat up. Dont ask me why, but if the sump level gets too low it also heats up. I had a dart in almost the same position on a 150 gal rubbermaid and it would heat up when dirty or the water level was too low. Does yours shut down, or just feel hot? Make sure the fan clean and is turning freely. Mine got a piece of eggcrate stuck in it once.