Oil burner intermittent fault and puffback

Old 01-13-15, 04:43 AM
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Oil burner intermittent fault and puffback

I have an older (1987?) Williamson oil burning furnace. It has a Beckett burner re-badged as a Williamson 02-693. I had it professionally serviced and it was running well last year and only reset probably once the entire season. At the end of the season I was stupid and let it run out of oil. This year I changed the tank filter, pump strainer, nozzle, and air filters myself. The burner wouldn't fire and would trip the Honeywell control after about 8 seconds or so. I disconnected and blew out the line from the tank with compressed air and re-primed the pump. I then determined that the pump was getting oil and producing pressure but the gun was not seeing any pressure. I looked at a pump diagram, took the pump apart, cleaned it, and rebuilt it. When I installed the pump the burner fired fine and I thought I was done. Since then I have been experiencing intermittent safety switch trips anywhere from once a day to once a week. I have noticed that while the burner usually fires almost instantly after the motor turns on, sometimes it takes a few seconds and there is bang, rumble, and a little bit of smoke comes out around the observation window lid. I believe this is called a puffback.
Last night I replaced the pump with an identical one from a used burner. It fired and ran fine but then tripped again sometime in the middle of the night.
the CAD cell looks OK, the electrodes look OK, the nozzle is a .85 80deg and was new this year. I noticed a little bit of oil in the air tube under the gun. It looks like it has been dripping and evaporating leaving a small puddle and some black buildup.
I have not witnessed what happens when the furnace actually shuts down so I cannot comment on the events that lead to a failure. What could be causing my problems?
Another note, I tightened up my basement a lot since last year, but the house should still be nowhere near airtight. I know this can sometimes impact natural draft appliances.
Old 01-14-15, 09:29 PM
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I'm thinking weak ignitioin transformer. Sorry for the slow reply. I somehow just plain missed your question.

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