I have An ArcoAire (Snyder General) HVAC:
Model #:GUA080A016-IN
Serial #0000246426-P05-0106

I have a flame rollout in the #2 combustion chamber that begins at 2-3 minutes after the main blower starts.I was having a flame rollout in both #2 and #3 that began immediately after ignition. I had the unit professionally cleaned/inspected, which eliminated the #3 problem. The tech found no cracks in the exchanger. The flue is clear. There is venting at the #2 exhaust. The combustion fan is running and appears strong. We even tried removing the baffle at the top of the exchanger. Still, the tech was unable to diagnose the problem and recommended replacement. Any suggestions?