Incomplete: 2 System: worked on right side of home. Trane Gas Package unit came to perform EPA and found back up heat GaS LP not coming on: Found burnt flame sensor wire repaired it also found very rusted burners. Cleaned them and flame sensor. A lot of rust was coming out of heat exchanger. I turned unit on and the flame was rolling out severely. Found cracked Heat Exchanger. Need to replace heat exchanger and two burners: