Combustion question

tylerjgardner

Hey so today I went to an oil Furnace Service call and was getting a combustion reading at the end. I understand as long as CO levels are under 100ppm in the exhaust its fine, but I thought under 50 is ideal. What would cause these elevated levels? (See photo). I have -0.02" of draft over fire, pump pressure at 150 psi and had a .50 60B nozzle in there. It was a beckett AFG burner. L head if that means anything.

Yesterday I did a maintenance a year after the install. And I was called back today because they had no heat. It was on lockout. I check oil flow and it was good. I fired it up and it seemed to be rumbling and then the flame went out. Long story short I had to bring the Co2 from 11 to 12% and that made the difference. Can someone help me understand why choking off some oxygen stopped the rumbling?

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HVACNUT

What model furnace? I had one recently. New installation no heat on a Boyertown furnace, Beckett AFG with the L head.

Combustion test beautiful. 0 smoke.

It came back in the next day no heat. There's oil on the L head. I reset and it fires right up. Combustion test numbers are different. O2 and excess air went way up. I pulled the burner. Got the T-Gauge and checked the Z dimension. The assembly was 3/4" back from specs. I set the Z and dialed it in. Haven't heard a peep since. Check the Z dimension.

HydronicMike

What was your smoke test reading?
What was your excess air?
What was the outdoor/indoor temperature of your first combustion test, and the recent one?

I’m guessing when you set it up the first time it warm weather and you didn’t allow enough excess air.