A little knowledge can be so dangerous.. my trane stopped working, I did a search and found someone with the same problem and they were told to disconnect and wire together their high temp limit switch (middle bottom of the pic with the two yellow wires going to it... So I did that, now it works, yet what part does that mean I need to replace? The circular part at the top of the pic with the barcode on it?

http://i250.photobucket.com/albums/gg267/Suffocate1_photos/trane_zpsdfava2bz.jpg (http://s250.photobucket.com/user/Suffocate1_photos/media/trane_zpsdfava2bz.jpg.html)

No you don't need to replace that. Check to make sure your filter is clean. I wouldn't run it very long with the Hi limit bypassed. It's probably an air flow problem.

The round part at the top is the pressure switch. You need to replace the rectangular device with the 2 yellow wires, next to the gas valve.