Yesterday when I was doing a water change on the 65g Malawi mbuna tank in our kitchen, I noticed the water seemed really warm, so I measured it and it was 88* F. The fish didn't seem terribly stressed, but since I was doing a water change anyway, I dropped the temp and chalked it up to the fact my wife had been cooking and baking all day and the kitchen was warm (though I was disconcerted, because that is still much warmer than the room).
Tonight I see the fish behaving a little strangely (kinda lethargic, and hanging out near the bottom not moving much - odd behavior for mbuna), so I felt the water and again, it was really warm - 92.8* F !!! I look at the heater, and despite the thermostat being set to 79* F and the tank being nearly 93, I can see waves of heat coming off the thing. As I'm trying to drain the tank now to do another emergency water change to drop the temp, one of the Labeotropheus trewavasae 'Jenwilliamsi' has literally gone belly up.
Needless to say, I unplugged the heater, and hopefully my fish will recover from this after the water change. This was one of the slightly older models of Stealth Pro, before they put the Green/Red LED lights on the top. And at least it didn't explode and shock me or crack the tank, but still, I would prefer that the only fish in my house that are properly cooked are the ones on my dinner plate (ironic, considering we had salmon for dinner).