What failure symptoms indicate replacement of an oil furnace ignitor transformer?

Common symptoms include delayed ignition, repeated lockouts, weak or intermittent spark, and ignition that works only when warm or only in dry weather. You may see carbon tracking, cracks in insulation, or burnt odor around the transformer. Audible snapping outside the electrode area can indicate HV leakage to ground. If correct electrode gap, clean electrodes, proper grounding, and good cables are confirmed, but spark remains unreliable, the transformer is suspect. Because HV insulation failure can worsen quickly, replacement is usually preferred over repair.