Williamson high boy low boy are just the furnace (aka air handler), the burner are usually other brand manufacture. mine was Williamson HighBoy Unit. Oil burner is the Caroline but Beckett seems to be more popular. having said that. It is easier if you note the model and download their manual to trouble shoot.
It will be hard to trouble shoot without being there and with that statement with no information (burner, filter, what event leads to this), or know your background what you have done. Might cause a bigger mess if you are not comfortable with working on them.
Example, I think some guy asked what was wrong with his gas furnace intermittent flame issue and swear to everyone that he test voltages with pictures. then later find out that the wire was just loose....somewhere on the same line he tested voltage..... so if you get frustrated you might want to get a professional or what ever they are called.
Here are some basic checks I can think of when I was trouble shooting my furnace. Might be more if people think of and add.
Fuel related.
Did you have fuel in tank? --> think you answer that. Fuel in tank is not necessary fuel in line especially if it is clogged or have a air pocket in the line. some reason most pump are not good enough to pull fuels if there are a large air pocket say after a filter change and more than hand full of fuel got out of the line.
Did you tried to change the oil filter and forgot to bleed it ?
Was the filter changed recently maybe it got dirty?
Did you have fuel delivery that stir up a sludge on bottom and clogged up the filter or running the tank close to empty...?
Did the motor run?
Do you have spark? usually systems are configured when motor runs also power is supplied to the ignition transformer.
If it is check if you have power to the ignitor transformer that produce spark. just be careful at that area. It's a most of these burners are 24V AC for control circuits, and 110V for burner/transformer(also have 10,000Volt) /motor/power vents.
Did you mess with the spark gap ?
Does it have flame initially ?
Did it go off after 2 minutes ? --> if it is check the resistances of that photo sensor / flame sensor. Try cleaning that lenses. Resistances should be in mega ohms then once it sees flame or a bright light shine to it, it drops to 1K Ohm or less. Maybe it was the other way around.
Is the nozzle clogged ? ---> first you should make sure there are fuel coming out of the bleeder valve from the filter and from the pump. but I think you mention no fuel from the bleeder valve ?
what was the primary control unit model number (the one that red reset button attached to) there are relays inside it as well might be burned out if it does not work completely. did you test if you have 110V at the proper terminals after it is call for heat. Unfortunately you have to trace the wire diagram.....,,, to trouble shoot further if it is beyond the spark / nozzle / flame sensor/ motor / transformer. Best way to start is find out your burner model. Not the air handler (Williamson)
Other misc:
Do you have a power vent? Mine was the power vent control board were burned out this past winter, the copper traces were fried. I had to re-solder it back since the local wants $500 to replace the whole unit. and order online just the board took weeks on the coldest day is not good.
Good luck.
