About a month ago I bought a temp controler, with it I am able to use my fans as "cool" and my heater as "heat". Now since the heaters are no longer fighting the fans, I was able to remove one of the 300 W heaters, and save power. I put the heater I removed in a drawer where it would not be damaged.
Yesterday I was preparing for a large water change on both my tanks, mixed in an acrilic tank I have laying around. My normal 50W heater was not going to heat this much water so I pulled out the heater I had in my drawer, taken from my main tank 1 month earler. When I went to bed it was working perfectally, brought the water up to temp and was maintaining it there, when I woke up the water was up to 87.9 DEG

and the heater was locked on.
Imagine if it had done this before I had the temp controler! A heater locked on combined with the heat of all my pumps, lighting and skimmer, especially because the fans used to shut off with my lights!
Just complaining, and very glad the heater waited until now to blow!
Whiskey