What would cause a impeller magnet to swell?

[Intheflesh]

I am assuming the answer is heat. I have a tunze hyrdofoam (I believe that's the model) that after turning it off, I noticed had a hard time staring back up. And when it started going, I noticed a weird noise. I turned it off and took it apart to find that the magnet had swollen. No worries, I think to my self, I have a replacement In the garage. I go to the garage , and turns out my replacement impeller is swollen even worse! Now I have 2 tunze pumps and no impeller. I realize that I can buy replacements, but I am curious as to why they failed? How do I know if there is something wrong with the pump itself? I don't want to go out and buy another impeller if it's just going to fail again, you know?

Right now I have both pumps sitting in a bath of vinegar trying to breakup what ever deposits may have built up. I did notice in one of the pumps, there were a bunch of tiny platic black balls, almost like bearings. Any clue what they might be?

 

[s_kelley]

I had this happen on koralia pumps in the past. Is the magnet coated with some sort of plastic? They told me that heat and soaking them in vinegar wears the plastic thin and splits or swells it. Koralia sent replacements for free so it might be worth sending tunzee a email

 

[Intheflesh]

Hmmmm good thought. Describes happened perfectly. the magnet is coated with plastic, and has thinned and cracked laterally.

I was worried at first that maybe the heat caused the pump bodies to warp as well, luckily they 'feel' ok

I think may cross post this in the tunze section of RC and see what they say