Furnace displays E15; burners ignite but shut off quickly; may indicate improper flame sensing or polarity

Safety first: Turn off power before working on wiring or flame sensor.

• Clean and reposition flame sensor: Remove the flame sensor, clean the rod with fine abrasive pad, and ensure it is reinstalled so that it is fully engulfed by the burner flame.
• Check ground and polarity: Confirm that the furnace chassis is solidly grounded and that hot/neutral are correctly wired (see E10 procedure). Flame sensing relies on proper grounding.
• Inspect burner ground: Ensure the burner rack has a good metal-to-metal connection to the furnace chassis. Remove rust or paint under mounting screws if necessary.
• Measure flame signal (advanced): Using a meter capable of microamp DC, connect in series with the flame sensor lead and measure during burner operation. Napoleon controls typically require a minimum flame signal (e.g., >1–2 µA). If low, improve grounding and sensor position.
• When to replace: If proper flame signal cannot be achieved despite clean sensor and good ground, the control board flame sense circuit may be defective and require replacement.