Gas and Oil Home Heating Furnaces - Weil McLain ignition problem

I have a Weil-McLain WTGO-3 Model AFG. The burner fails to ignite when the system calls for hot water and I must push the reset button to start the furnace. I have replaced the oil filter (General 1A-25), the electrodes and nozzle (.75@80W). I have also removed and checked the oil pump screen (clean). I removed the flue pipe and checked for soot. Minimal soot was detected. I cannot understand why the furnace will intermittently go on safety and fail to ignite. There is a Honeywell R4181D Primary and an L8124A,C Aquastat. This problem has only started within the last week.

Sounds like time to get a good Oil pro in to go over everything, sounds like it's either over or under fired. That can't be done by eye.. Must have equipment to check Smoke, Draft, Stack Temp.. ect..

When was the last time you had a pro in on this?

Service Tech looked over the system last February. Everything mentioned earlier was replaced except the oil filter screen. Smoke and draft test was performed. I don't know if a stack temp test was done.

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I have replaced the oil filter (General 1A-25), the electrodes and nozzle (.75@80W).

You sure you have everything set right?? (the electrodes and nozzle) Did you check the transformer out is it good. Can you pull a 3/4" spark on it
Do you know how?? Is the pump psi good ? Nozzle set right to the cone? Is there oil in the unit when you reset it? You can have so many things that you have to check. Id call a tech.

As Ed mentioned, the electrode settings could be off. They should be 7/16" above the center of the nozzle, 1/16" out past the face of the nozzle & have a gap of 1/8" to 5/32".

The ignition transformer is easy to check but you have to be careful because it packs 10,000+ volts & bites hard if you are careless. To check it, disconnect the small tube going to the nozzle assembly & aim it into a can. Start the burner & flip open the transformer. Lay the blade of a screwdriver with a WELL insulated handle across the two springs & while keeping contact with one spring, draw the screwdriver back toward the other spring. You should be able to draw the screwdriver back 3/4" before you loose spark.

If you removed the screw rather than just the lock ring when you removed the nozzle assembly, the assembly may not be positioned correctly.

Transformer has plenty of spark. I repulled electodes and reset them. Initially this seemed to solve the problem. The furnace started and came up to temperature. I even raised the room thermostat to 76 to kick in the baseboard heat. The furnace kicked on once again, but then that was it!! Now, it will only start when the reset is pushed and will only come on for one minute before it "clicks" off. The flame appears to be good throughout. Please give me any ideas you may have before I set the entire unit on a barge and give it a "Viking Burial". Incidentally, the unit was replaced in 2002.
Any advice will be greatly appreciated. Thanks!

My wife called the oil service before I could "launch" the furnace into Lunar Orbit. He came while I was at work and fixed the problem within minutes of his arrival. According to my wife, the problem was a loose wire on the photo cell!!!! The burner seems to be working perfectly now.
Anyway, I wish to thank you for your advice. Is there anyplace where I can learn more about the intricacies of oil heating appliances?

Once you said the flame appeared to be stable & the burner locked out after a minute of run time, I knew it was a flame sensing problem. On to education:
Many community colleges or local vocational schools offer a 6-9 week evening class (usually 1 or 2 evenings/week) on basic oil burner service. These classes are generally geared to the homeowner who wants to do his own troubleshooting & routine maintenance.

This can help some . But like said it takes school and years before you get it right the first time.

http://www.freepoolheat.com/oil.html ;)