Abstract: Improved apparatus and method for selectively monitoring the light intensity emitted from an oil-burner flame for purposes of determining when the burner is in need of preventative maintenance. The apparatus features a monitoring system including: a sensor for detecting burner, flame-light intensity; a comparator for comparing the light intensity sensed to predetermined upper and lower limits; a display for indicating whether the burner is operating acceptably or whether it requires maintenance; and a discriminator for selectively coupling out-of-range, intensity indications representative of a need for maintenance to the display. The discriminator includes measurement-threshold circuitry for determining whether the burner has successfully ignited and whether the flame generated has been sustained long enough to assure thermal stabilization.