Dolphin pump stuck impeller

[bromion]

I have a Dolphin Ampmaster external pump running my closed loop. Sometimes when it's off and turns back on, it gets stuck. The impeller shaft won't turn without help (a wrench!). Sometimes this makes the pump get very hot.

Any suggestions on how to fix or prevent this? Any danger of causing a fire??

I recently opened the wet end, cleaned and resealed it (seal was leaking). This problem has been happening for a while tho, long before the cleaning and resealing. I was hoping that would do it.

Thanks for advice.