Something may have bent the shaft or the added heat could be warping the magnet. If you haven't done so lately, you may want to open the propeller compartment and give it a good cleaning. At least once or twice a year it's good to give the submersible pumps a scrubbing and soak in some vinegar water to remove crud and mineral buildup. I learned this the hard way. Three years ago, I had a mag18 seize up and it warped the entire pump case. However it's sister pump(8yrs old) is still going strong.