I was given 2 small space heaters that didn't work. I traced the trouble to a small resistor looking thing that allows voltage to pass unless it gets to hot then it opens and shuts the heater off...a safety feature. I don't know where to find these because I'm not sure what they are call...thermistor?..thermocouler? the markings say UPO BF84 and below says 84c. I cut them out and straight wired and the heaters work find but I would like to put the safety feature back in...any suggestions where find some of these.