Oil furnace not working. Was working. Ran out of oil. Filled the tank. Now the furnace won't run. What's up?

Air in line, filter clogged, in older oil furnaces there is a pot that needs some oil put in them first to work. Little float in there, Been the 70s last I had oil heat. But mine was that way. You added the start oil to the pot with a long handle spoon then restarted the furnace.

You need to bleed the air out od the fuel line. Disconnect the fuel line from the \Furnace and let the oil come through the line, then re connect it tto the furnace.

May need to purge air from the supply line, at the end near the burner, so the pump can draw the liquid fuel. Fuel pumps don't move air very well.

Thanks for the update. Y!A no longer allows you to delete a question once there is an answer posted to it. You can, however, award "best answer" to someone, which changes the status of the question, not to mention signaling something about which answer helped the most.

Most likely cause is an air dam in the fuel line. The air must be bled out of the line going to the burner before the pump can push the fuel into the burner. A very common happening when the fuel runs out.

Maybe the line that comes from the tank and feeds the burner assembly has gotten an air bubble trapped in it when the tank was empty. Maybe you have to bleed the air out of the line.

Good habit to get into is to not allow the tank to ever get fully empty!

You need to bleed the fuel line. There will be a small screw plug that you can remove and let the air out of the fuel line. Once the oil starts coming out screw the plug back in. Wipe up any spillage and your boiler should be good to go.

I'm guessing the pump lost it's prime and isn't actually pumping the oil to the burner.

Maybe the motor siezed when it tried to run without any oil in it? Try calling a furnace technician to "diagnose" the problem.

is the filter clogged? since you ran out of oil, it may have brought up the muck from the bottom of the tank

Repair technician will diagnose the problems and repair them.

Plenty of reasons NOT to work