If the house is 40°F indoors, which is less than a normal living environment, could it be preventing a consistent draft in the flue that the exhaust normally follows? Heat in the house would normally try to escape through this vent. Is the side shot power venter something that induces a draft for the flue? If so, perhaps this is not running properly when it gets really cold?

A power venter is a motorized fan, but I was also thinking that lack of draft on very cold days was the answer, but a power venter eliminates the chimney and isn't affected by temperature.

Your cad cell eye is supposed to shut down your burner within 15 seconds of "seeing" a smoky fire....and they don't reset on their own, meaning that your burner would not start again until someone pushed the reset button.

On the other hand, maybe the fire is clean, but the venter can't exhaust the fumes, but a clean burning fire won't make soot.

Call an alarm company. There are devices which can monitor your situation and call you, but I don't have any names for you.

You can't convert to propane without removing the oil burner and installing propane and your boiler must be able to accommodate that changeover.

Where is the oil tank located? In or Out?

The oil tank is outside underground and 4 years old. Thanks

"Outside"! Are you using #2 fuel oil or kerosene?

Fuel oil will gel when cold, kero won't. I don't know at what temp fuel oil starts to gel, but it might be causing you problems. You can get an additive to add to #2 or you could use kero, which burns much cleaner.

Most outdoor tanks have kerosene for fuel. (above ground, anyhow)

It starts to gel about 20 degrees, but if the tank is underground, I wouldn't suspect that.

In any event, the oil will have a long time to acclimate once the line goes through the wall into the basement area.

You have an odd situation. Maybe a small piece of the puzzle is missing.

Well, it might not have that long to acclimate, even though it gets into the house.

"it has happened during very cold snaps in deep winter

Like how cold? Zero degrees coming into a 40 degree environment inside, still could be a problem. ... even if it gets inside. How deep is the tank buried?

I asked a few other people about this and the consensus is: The very cold days were probably very windy and if the vent is facing either north or west, the wind overcame the power venter and thus the smoke.

You don't say that the burner shut down on safety, so I am assuming that the house became full of smoke and the burner started up normally in the next cycle, which is in line with the windy day theory.

I don't think fuel gelling has anything to do with it.

Again thank you for the help.

The windy day theory crossed my mind along with the fuel oil jelling.

But,with the wind blowing the smoke in I did not think it would cause a soot condition in the boiler, just fill the house up with a fairly clean smoke.

The boiler completly sooted up after both events causing such a thick smoke the fire company had to brake into the house both times.

And with the oil jelling I thought the oil burner would shut down if it was not receiving a good oil flow.

I could be wrong on both accounts

The tank has been filed with fuel oil and not kerosene.
The top of the tank is about 3 feet down although I do not think the line feed and return lines are very deep and run about 10 feet to the house and then only 3 feet to the boiler in under the house.

This adds a little more info to the story. So we have very cold weather and a sooty fire. Does the burner shut down from the sooty fire and have to be manually reset before the burner will run again? The primary control should shut down a sooty fire in 15 seconds.

The oil burner never shut down both times.

Again he whole system has always been cleaned and serviced
every fall and the problems happened in feburary.

After the last backup I did replace the whole oil burner with a new unit.

Do you know of anyway to test the burner to see if it would shut down under sooty conditions.

Also the reason I am on here asking all of these quetions is I have had at least 4 different service tecks out and they all seem to know less then me, which is not much. Thanks.

I think, the photo cell basically looks for "flame". I know, they can get pretty murky on the lens and still function.

I just happened to think, "power venters" are supposed to have a proving switch, aren't they? In other words, the air flow through the flue/vent is supposed to be established, before the burner kicks on. ??

Here is a link that might be useful: Field Controls power venter

We have a lot of fuel and heating customers with seasonal camps and vacation homes. Your issues are a classic example of why I don't recommend power-venters in seasonal homes unless someone is around to check on them. With a chimney you have a large margin of error and no potential points of mechanical or electronic failure. With chimneys there are no issues caused by wind currents, poor burner setup or snow levels. Plus they're never installed under decks, under windows or hidden in the bushes.

The soot issue might simply be a boiler and burner setup issue. The power venter is effectively an artificial mechanical/electronic chimney. While power-venters are functional, they can't overcome poor oil filtration, poor boiler/piping design, poor burner setup and they're no replacement for qualified professional technicians that know how to use their electronic combustion test equipment.

Replacing a 4 year old burner sounds fishy. What brand and model of boiler and burner do you have? Does the boiler have a tankless coil that produces hot water? Do you have a two-line oil system or a single line system with a Tiger-Loop?(With a 2-line system you're constantly circulating cold oil through the lines, filter(s) and strainer) Do you have a decent spin-on .10 micron oil filter? Is the boiler oversized (short cycling)?

Pictures of the boiler and piping would help if you have any from a few angles.

Concerning safety monitoring devices, I know of freeze alarms, water alarms, low fuel alarms and smoke detectors that dial out to telephone numbers in the event of a problem, but I guess you'd be looking for a smoke detector with relay that would kill the power to the burner.

Yes, cad cell eyes look for flame, but the resistance built into the eye is affected by the intensity of the flame. If a new eye is installed and isn't aimed properly, it will see a flame, but not properly and will go off on reset. Even external light sources from a poorly sealed ignitor will affect the eye's function.