exploding heater

Question
I just set up my new equarium and had it running for a few days. I just added a few fish and a snail and everything was going perfect. I left to go up to bed and heard a small crash and assumed it was my dog and it didnt sound that bad, so i went to bed. I woke up in the morning with steam coming off my aquarium. The temp. was higher than my thermometer could read and all my fish were dead. The heater had exploded and was in 10 peices. Can you explain to me what happened? It was fully submerged and wasnt touching anything.
I obviously need a new heater, which do you recommend?

Answer
I would guess one of two things, first water seeped into the barrel of the heater, was vaporized and boom.
Two, the contact inside the barrel stuck and the heater went into the nuclear zone.
I would check out Aquarium Pharm. there heaters are good middle of the road heaters, get a complete submeriseable one.
If you prefer annother brand, get what you like.
Get the next size up from the recommedned size for your tank.
If you have more questions, just ask