Lochinvar & A.O. Smith 100112678 Flame Sensor

The Lochinvar & A.O. Smith 100112678 Flame Sensor is a critical OEM safety component engineered for precise flame rectification in high-efficiency boilers and water heaters. Designed for Lochinvar Knight and A.O. Smith B4940, B5930, B5940, and B7930 series units, this sensor monitors the burner's ionized path to ensure the gas valve remains energized only when a stable flame is present. Constructed with a high-grade Kanthal or equivalent alloy rod and a durable ceramic insulator, it withstands the intense thermal cycling of modulating-condensing systems. If your diagnostic shows low microamp signal (µA) or a 601/602 lockout code, replacing the fouled or oxidized 100112678 sensor is the standard protocol to restore reliable ignition sequences. This genuine A.O. Smith replacement part ensures impedance matching with the proprietary control board, preventing the nuisance short cycling often caused by non-OEM alternatives. Verify the grounding spade connection is clean and secure during installation to maximize signal strength.

• OEM Compatibility: Exact replacement for 100112678, ensuring proper fitment in Lochinvar boiler burner plates.
• Direct Flame Rectification: Provides high-accuracy microamp feedback to the ignition module for rapid flame verification.
• Durable Construction: High-temperature ceramic base prevents electrical leakage, even in high-humidity condensing environments.
• Safety Integrity: Prevents unburned gas accumulation by immediately signaling the gas valve to close upon flame failure.

• What does a low flame signal (µA) indicate? If the sensor reads below the manufacturer’s threshold (typically < 1.0 µA), check for carbon tracking on the ceramic or soot buildup on the rod.
• Can I clean the 100112678 sensor instead of replacing it? While steel wool can temporarily remove oxidation, the metal rod thins over time, leading to resistance changes; replacement is recommended for long-term reliability.
• Why is my boiler short cycling after ignition? If the flame lights but drops out after 2-5 seconds, the flame sensor is likely failing to send a rectification signal back to the board.

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Disclaimer: While we strive for 100% accuracy, product data and specifications are subject to change. Please contact our team to confirm compatibility or technical details before purchasing.