Oil furnace lock out mystery

Ddtar

I've been having trouble with my oil furnace for almost a year now. The local oil company has come in and replace multiple parts and cleaned it out many times and I think the only thing they haven't replaced is the motor. 
Basically what happens is it goes into hard lockout mode. It's pretty easy to fix just by pushing the button but I don't understand why it goes into this mode and they've even replaced the controller on the furnace itself. Here's the strange thing it pretty much only happens once the weather starts to get cold. So I basically had no problems all summer long except for maybe once for some strange reason but now that it's starting to get cold out and we're using the heat in the house it's happening. It's really frustrating and annoying to have them keep coming out and trying to fix it when everything they're doing hasn't made any real improvement. Does anybody have any ideas?
I am losing my mind!

EBEBRATT-Ed

Yes, I do have an idea. A new service company that knows what they are doing. And they are hard to find.

You could post where you are located and check"find a contractor" on this site, maybe someone is near by

Can you post some pictures of the furnace & oil tank so we can see what you have?

Is their a slip of paper around the furnace like a combustion test?

Can you tell us what they replaced? That will give us a clue

STEVEusaPA

You could also install a primary control that has on-board diagnostics on it to maybe help point you in the right direction.
They also make a tool called an On Watch. Not too many people still own them. It’s a data logger that attaches to every component on the burner and monitors all the cycles.
When you tell me it happens when it’s colder, to me that indicates it may not be set up properly, especially combustion air and draft.
Could actually be the motor. It’s easy to test. Could even be a cracked heat exchanger.
But like @EBEBRATT-Ed said, you got to find a competent tech.

EdTheHeaterMan

Anyone who has done oil burner service for an oil dealer has come across this type of unexplained nuisance lock out call and the cause can very. I have come across an ignition transformer that fails after it is operating for 30 minutes or so. On the old 3 wire primary control, the ignition transformer is powered whenever the motor is powered. As it gets colder the transformer is powered longer and the windings heat up and cause an open circuit internally. On the next on cycle, there is no ignition and the burner fails to ignite. By the time you realise there is a problem , the transformer cools down. The open circuit resulting from the heated windings has cooled and the circuit is closed and operated just fine.

Another is an open winding or dead spot on the motor also resulting from a warmer motor that is operating longer as a result of colder weather. Same thing, when you get there to reset, everything is cooled off and the open winding makes a connection and it seems as there is nothing wrong. There are any number of things that have caused this problem from clogged filters to a basement light being left on and shining a small beam of light on the pristine white surface of a combustion chamber as it passes thru the inspection port of a boiler. That spot of light fell on the chamber wall in just the right location for the cad cell eye to detect it. As soon as I stood between the basement light and the inspection door, the burner would start. As if by magic, my mere presence in front of the burner caused it to start.

Today the Carlin 70200s universal primary control has some diagnostic features that will help a trained technician pinpoint the cause of the problem. If the problem is ignition, or loss of flame signal during mid cycle, this will rule out some items and guide you the the most likely cause. In my last few years as a troubleshooter, I have found that control to be most valuable in solving the "Fantom Lockout" problem on several customer's oil burners

I hope this helps.

Yours truly,
Mr. Ed

Big Ed_4

You can throw up all the thermostats , run hot water and sit there and cycle the burner though the service switch until the problem shows itself ...

Jon_blaney

I have had this issue on several different oil burners. Once it was the ignition transformer, the other time it was the points. The points get hot and expand out of tolerance. They cool and return to proper gap.

STEVEusaPA

Jon_blaney said:

I have had this issue on several different oil burners. Once it was the ignition transformer, the other time it was the points. The points get hot and expand out of tolerance. They cool and return to proper gap.

I've never heard of that. The electrodes can't expand/contract that far. If they did it would be something occurring all of the time. I doubt they even move a millimeter, if that.

MaxMercy

STEVEusaPA said:

Jon_blaney said:

I have had this issue on several different oil burners. Once it was the ignition transformer, the other time it was the points. The points get hot and expand out of tolerance. They cool and return to proper gap.

I've never heard of that. The electrodes can't expand/contract that far. If they did it would be something occurring all of the time. I doubt they even move a millimeter, if that.

Agree. Thinking more along the lines of an old style transformer that might weaken as it gets hot. Closer gapped with sharpened points might allow a weak transformer to work where a new trans or electronic ignitor would work on rounded wider gaps.

HVACNUT

It was more common on primaries with intermittent (constant) ignition. 

EdTheHeaterMan

HVACNUT said:

It was more common on primaries with intermittent (constant) ignition. 

Showing our age. "Intermittent formerly constant" printed on the box the Honeywell control comes in, back in the 1980s