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Bart Jay
Bart Jay, HVAC Technician
Category: HVAC
Satisfied Customers: 655
Experience:  35 years in HVAC. NATE Certified EPA certified
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I have a Ducane oil furnace. I have replaced the filter and

Customer Question

I have a Ducane oil furnace. I have replaced the filter and nozzle and within 1 day to 1 week I get a carbon "donut" around the vanes that swirel the air where the flame sprays out. This shuts off the flame sensor and the furnace dies. I have tried .75/80degree A and B nozzles. It did it last year and I made the same repair and it ran for a year until it ran out of fuel, now I get the carbon again.
Submitted: 5 years ago.
Category: HVAC
Expert:  Bart Jay replied 5 years ago.
Do you have the correct nozzle installed based on the label specs of the unit?
Customer: replied 5 years ago.


The spec is .75/80degree solid(B). The furnace calls for B (solid), but as a low flow (.75gph) I tried the A (hollow) looking for a solution. . The A type nozzle is what worked for the past year. Then I ran out of fuel, filled up the tank, let it settle, changed the fuel filter and nozzle with the correct nozzle 75/80B and restarted the furnace. A donut sized carbon ring appeared in 1 week after replacing with a B, shutting down the furnace probably because the light sensor couldn't see light, so I went back to the A. It lasted a day and the same thing occurred. The problem is not nozzles at this point.

Expert:  Bart Jay replied 5 years ago.
It may be that the entire nozzle assembly needs to be moved forward. If it is back to far the oil may be impinging on the ends of the blast tube. Move the assembly forward and adjust the air for good fire.
Customer: replied 5 years ago.

sorry, nothing has moved. it is all very rigid.


I siphoned contaminents from the bottom of the oil tank, changed the filter and nozzle once more and it is running. There was algea of sorts blinding the filter, and that restricted flow, and caused the problem. The furnace is now running normal for 3rd full day. This issue is closed. I did not accept your answer.

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