Ran out of oil the other day and boiler went on lock out. I got the tank topped up today, pressed the reset button and tried to fire it up but it just keeps going on lock out after about 12 seconds.
It appears you may have an air lock caused because the oil feed in the pipe ran out and the new oil has trapped air in the pipe leading to the pump. You need to bleed the pump. There is a nipple which you open and then as soon as oil appears tighten this back up but DO NOT HAVE THE BOILER OPERATING WHEN YOU PERFORM THIS. The oil will appear of its own through gravity.