Why did sparks come off my oil burned when I was trying to bleed it?

I had loosened the bleed screw, turned on the burner and pressed the restart button. The burner came on and then sparks can off the top of it.I did'nt get any oil out - it was only on for 20 seconds maybe so probably not enough time or maybe it was'nt loose enough.Why did sparks come off my oil burned when I was trying to bleed it?
What are you trying to do? Im not sure what you are talking about.

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