Turn off the circuit breaker to the heating system.
Open the heater. Locate and open the black box where the electrodes are located. Look at the tips carefully; this is where the spark fires to ignite the oil. If the tips are corroded or covered with soot, clean them with alcohol and a soft cloth.
Examine the electrodes for cracks. If you find cracks, the electrodes must be replaced.
Check the connection between the electrodes and the oil burner. Any corrosion or loose connections must be addressed. Remove corrosion with alcohol or a solvent, and tighten the connections between the electrodes and the oil burner.