Problems that prevent an oil furnace from starting include inadequate oil in the tank, clogs and air bubbles in the pipelines and faulty burn motors. According to HVAC For Beginners, the most serious possible cause of furnace dysfunction is a dry oil tank, which creates several other potentially serious issues. Many non-starting furnaces require professional service.
When the oil levels in a furnace grow dangerously low, sediment accumulates in the pipes that connect the oil tank and the furnace itself. Left unnoticed, the problem becomes progressively more serious and more expensive to fix. In extreme cases the sediment blocks the pipe, depriving the furnace of oil. Air bubbles cause similar problems. They form when the furnace runs out of oil, leaving its pipes empty. When fresh oil enters those pipes, a pocket of air sometimes remains.
Another common cause of a non-starting furnace is a faulty motor. Motor repair and replacement require professional intervention. Clogs and air bubbles, however, often respond to home remedies. The easiest way to remove a sediment clog is to push it back into the oil reservoir with an inexpensive pipe plug. To remove an air bubble, open the furnace valve and release a small amount of oil. This also eradicates the bubble.