Omni Econo Heat 150k btu Waste Oil Burner

Hey gang, looking for some insight/advice/reviews of an Omni Econo Heat WVO furnace. I installed one 3 years ago in a warehouse at work. We are a Food/Meat/deli store that produces about 80 gal. of used canola oil per week. The oil is used to cook fried chicken in a pressurized fryer, and I have learned over the years that the chicken fat will get emulsified in the oil and not precipitate until it's at the correct low enough temp.
That being said, this year the burner had been working fantastic through about 500 gal of last years oil, with 2 or 3 cleanings of the nozzle and vortex inducing baffle of the burner. about 2 weeks ago it stopped firing and we cleaned out the vortex blades and the nozzle and the area around it. since then it refuses to fire on our oil. It will burn house fuel, howeever. I called our HVAC guys, (they are pretty good at everything else), and after 3 days of working on it, they tell me that it is the oil that will not burn.
I have good oil flow, what looks like a good spark, and good air. I asked him if there could be a difference in the spark, via the transformer or the spark isn't "hot" enough. He told me that in his experience the transformer "either works or dosen't".
Has anyone else had this situation where the oil they were burning no longer burns? I;m at a loss at this point.

Thanks for any helo I may get<

John