Puff of fuel smell from barometric damper on startup

skybolt_1

The saga continues with my annoying AFG issues. (History here https://forum.heatinghelp.com/discussion/194271/beckett-afg-efficiency-testing-boiler-sooting-issue)

About a month ago I opened up the firebox and did my usual cleaning, paying particular attention to the heat exchanger fins. Overall, there was very little sooting. Fired up the boiler, did multiple smoke tests which all showed 0 smoke. Not ideal, but given the history here I'll take the efficiency hit to avoid sooting.

Each morning when I come downstairs to the basement, there is a smell of fuel oil. I have phantosmia, which is just great for problems like this, because I can never be sure whether I'm smelling what's actually there or not. I've had my FIL walk through the basement and he claims it smells "normal" to him for a home with oil heat, but it just seems wrong to me. I have ruled out oil leaks in the system. All possible leak points are dry, oil pipe from tank is new, there is no trace of leakage anywhere.

This morning I happened to be down in the basement, went into the boiler room to see whether I could figure out exactly where the smell was coming from. Sniffing all the joints / gaskets / etc. Sniffed around the barometric damper, nothing. Suddenly, call for heat. The AFG turns on, goes through it's 15 second pre-ignition routine, fires. Big puff of exhaust hits the barometric, right into my face - bingo. Strong fuel smell. Barometric then opens as expected to maintain draft.

What would be the most likely root cause here? Filters are all good, running a 10 micron and a Tigerloop. The AFG has a CleanCut pump. Brand new nozzle, precisely aligned electrodes. . I've eyeballed the firebox through the port at shutdown, see no evidence of any kind of lingering burn / drip. No oil in the air tube. No sooting around the barometric.

Jamie Hall

How's the flue? When the boiler is off and cold, how open is the damper? Can you feel any downdraught through the damper (unlikely, but worth asking) when the boiler is off?

EdTheHeaterMan

a slightly delayed ignition can be the cause. Are the electrodes properly adjusted? Is the nozzle partially plugged? Do you have too much excess air? (that can blow the spark cooler or the oil away from the spark) It could also be a combination to things. What are your combustion test numbers (I know you have a zero smoke) What is the over fire draft, stack temperature, and CO2.

Bob Harper

I skimmed through the other thread and my first question is the same as Jaime- describe the chimney, flue, height, diameter, liner, and chimney connector pipe.

If you have a tall oversized, cold, or restricted flue, you can get a lot of back pressure. 15 seconds may not be enough pre-purge. Go for 45 seconds. You may need to change the primary control.

Chimney draft readings should be taken btw the baro damper and the chimney- not just outside the boiler. That's where you take combustion analysis readings- about 1.5-2 duct diameters downstream of the appliance collar or any turns, dampers or draft controls. You should only need about -0.02 to -0.03 wci in the stack.

Once you've gotten your chimney in order, THEN tinker with the equipment.