Trane FUS 00620 fuse link
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I have a 26 year old Trane XL90 and this part went bad. Flame roll out. Breaks if the flame comes out into the furnace or it can just wear out. The part I know has been in the furnace for at least 12 years maybe more. Got the replacement part in two days.
After some quick and personal help from the folks at Keith Specialty Store I was able to identify the right part for my older Trane furnace. Apparently the nomenclature has changed (this used to be called a flame roll-over switch). The part was delivered right away, and the price and shipping were more than fair. Thank you, Keith Specialty!