Trane XE 90 occasionally short cycles until system lockout ( 2 flashes)

[oldFixer]

I have a 12 year old Trane XE 90 gas furnace. Occasionally ( once or twice a week) it will short cycle. When gas is called for, vent fan starts, igniter glows, gas flows, but sometimes only the first 5 of 6 inshot burners ignite. The 6th, which contains the flame sensor, does not always ignite causing the gas to shut off and the unit to recyle. Sometimes the 6th burner will ingite on the 2nd or 3rd try. If not the system goes into lockout (2 flashes)

 

[user 4883]

Clean the rail that provides gas to the "inshot" burners (most likely a spider nest or possibly some rust/dirt).
While your in there, might as well clean the flame sensor too. Some steel wool usually does the trick.

 

[keepinitcool]

Hey oldFixer,

I agree with kok328, i've seen spider nests cause this as well. I've seen these transfer rails on the inshot burners rusted up many times also. This is caused by the impurities in your gas supply reacting with the galvanized burner causing it to rust. This is a pretty common problem these days with the quality of fuel being supplied. A sure fix is to replace the galvanized inshot burners with new stainless steel ones and clean up that flame sensor at the same time. Not that expensive and will save you the headache in the future!