Gas burner flameout

RalphTaliercio

Hello,
I'm working on a Carrier hot air furnace with a five burner gas manifold. The last burner sometimes does not light causing the flame detection rod to close the gas valve. I put a manometer on the gas valve and the pressure is correct on both the first and second stage. It appears the gas is being pulled away before it can ignite. I put a perforated piece of sheet metal behind the last burner for testing and the burner consistently lights off, offering resistance to the excess draft. Someone suggested the heat exchanger could be cracked causing the draft issue.
Any Suggestions ?
Ralph

unclejohn

I would take the burners out and clean them. How did you get sheet metal behind the burner? Those burners connect directly to the manifold. Unless the indoor blower is running I don't see a cracked HX being a lite off issue.

ProblemSolver

Is your cloths dryer near by? Dust from it can get into the burners. When removing the burners, check the flame transfere ports that transfere the flame from one burner to the other.