Burner locking out

[snowdog35]

Having a very weird problem, I have a vacation home that is about three years old. It has a Nordyne downflow furnace with a Beckett oil burner, recently the last two times up we found the burner locked out. The first time I reset the burner & it ran fine for the five days up there. (Didn't notice if light was blinking on control). I assumed it was maybe a random thing. Well went up a few weeks later & the same thing (Noticed a solid green light on primary control). I changed the cad cell eye, primary control, oil nozzle, oil filter & electrodes, started it back up & it ran fine for the four days up there. While there I ask my local neighbor to keep an eye on it, about a week later he said it was down again. He had a local contractor come up, reset it & check. He said he could not find anything wrong. Now my question is this: Over the summer I put an A-coil in for future a/c & kept the blower speed at med-hi setting (Furnace originally came wired for high speed, I had lowered it a few years ago because of air noise through vents). Could the lower fan speed possibly lock out the burner gun if it goes out on limit? I thought I noticed the burner cycling on & off while calling for heat (T-stat was not satisfied yet). I was told by other people that it would not lock out the primary, only that the burner would shut off & come back on when the limit reset. Sorry for the long winded story, just going crazy trying to figure this out. Any advise would be appreciated. (Note: Oil tank is in basement & is two pipe system).
Thanks, Brett

[scooter-d]

Limit sounds like a good possibility. You'll need to check your temp rise. Get a probe type thermometer and check temp in your return close to the furnace (maybe in the filter slot), and the supply below the coil. I'm guessing the difference between the two should be around 60 degrees f. You can check the rating plate inside the furnace, probably near the burner box for the proper temp rise. And as I'm guessing you know, speed the fan back up if the temp is too high. If you have installed a new thermostat it could possibly be the cycle rate/heat anticipator that would need to be adjusted.
Hope you get it worked out soon.

[heaterman]

Limit won't cause primary lock out. There are numerous things that can cause this. You have already thrown (away) a fair amount of money at the unit by changing parts that were not the root cause. Since this is DIY and that's against site rules I can't go further into what to check. Intermittent problems can be the toughest to find and sometimes turn out to be the simplest things. A competent oil burner technician should be able to trace down and figure out the problem, especially since you have replaced that many parts and reduced the possible causes.

[firecontrol]

I'm going to guess here, but the fact that you didn't mention that when you reset the primary control the furnace rumbled, spewed smoke out of it and scared you that it lit off fine and basically normal.

If that's the case then that's what you need to tell a qualified oil service tech and he'll know the right places to look.