If you’ve tried the furnace reset button, checked to make sure there is fuel oil and your furnace still won’t start, don’t fret. Before you call the repairman or start shopping for a new furnace, check the fuel source and make sure the line to the furnace is void of air. Running low on or being out of fuel can cause a furnace to not restart even after you replenish the fuel supply. You may simply need to bleed an oil furnace line and start it up again.