I have no idea why the heater exploded. It was fine one day and then broke the next. I think it was just a cheapy one we got from PetsMart. Also, our pump didn't work quite right after that and we had to replace it as well. The only other problem we've had is that the grate in the top left hand corner gets clogged easily. When that happens there's not much water flow and the back gets pretty empty. It's not good to have a pump and heater running with almost no water, so I have to clean the grate every day when I get home from work. Other than that, I really like our nano. Unfortunately, it's become the "step-child" now that our 75 is up and running. So.......we're going to dump everything in the 75 and put the nano away for now. Good luck if you decide to get one!