I have a mag7, and it crusts up about once every 6 to 8 weeks. I keep 2 impellers on hand so it's just a quick swap out. If i don't catch it though it always chooses to go out at night, so i wake up to a tank with no water in the top 4 inches. Mine has froze up numerous times, and sat for hours froze up while plugged in, and never burned up. Just clean it up and plug it back in, that's what i like about mag pumps.