I have a Luxaire natural gas furnace, model PANU-LD20N160A. It is 20 years old. It breaks down at least once every season, and I figure out which part has failed or needs to be cleaned. Today I had to temporarily bypass a device or sensor and I'd like to know what it is called. It is on the "ceiling" of the fire chamber, located midway between the ignitor at one end and the flame sensor at the other. Two wires run to spade terminals on either end of it, and it looks like a small plate of lead solder between the wires. I'm guessing if the fire chamber got too hot, the lead would melt, continuity would be lost, and the furnace would shut down. I will try cleaning all the connections first, but if I need to replace this part, what is it commonly called?