House - Furnace Parts 69W43 Furnace Flame Sensor - Exact ForLennox, Armstrong & Ducane Furnaces
69W43 furnace flame sensor with white ceramic insulator and L-shaped metal probe.
69W43 furnace flame sensor replacement part shown with a furnace unit for sensitive flame detection.
69W43 furnace flame sensor with 90-degree bend and dimensions diagram.
Diagram of 69W43 furnace flame sensor highlighting the sensor head, ceramic porcelain, mounting bracket, and metal rod.
69W43 furnace flame sensor replacement part with white ceramic insulator and metal mounting bracket.
Technician performing a quick installation of a 69W43 furnace flame sensor with step-by-step instructions.
69W43 furnace flame sensor replacement part with mounting bracket and ceramic insulator.
69W43 furnace flame sensor with white ceramic insulator and L-shaped metal probe.
69W43 furnace flame sensor replacement part shown with a furnace unit for sensitive flame detection.
69W43 furnace flame sensor with 90-degree bend and dimensions diagram.
Diagram of 69W43 furnace flame sensor highlighting the sensor head, ceramic porcelain, mounting bracket, and metal rod.
69W43 furnace flame sensor replacement part with white ceramic insulator and metal mounting bracket.
Technician performing a quick installation of a 69W43 furnace flame sensor with step-by-step instructions.
69W43 furnace flame sensor replacement part with mounting bracket and ceramic insulator.
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69W43 Furnace Flame Sensor - Exact ForLennox, Armstrong & Ducane Furnaces

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69W43 Furnace Flame Sensor

Key Features

  • Sensing rod detects flame presence for furnace operation
  • Angled probe design
  • Overall width: 4-5/8 in
  • Features a 3/16 in male terminal for connection
  • Durable construction for long service life

Replaces / Cross-Reference Part Numbers

  • 69W43
  • 69W4301
  • LB-74940B
  • LB74940B
  • 102431-02
  • 790-801A1

Compatibility & Fitment

  • Direct replacement for specific furnace models from brands including:
    • Armstrong
    • Ducane
    • Lennox
  • Verify compatibility with your furnace model number prior to purchase.

When to Replace

  • Furnace starts the ignition sequence but shuts off after a few seconds.
  • Furnace control board indicates a flame sensor fault code.
  • Visible carbon buildup, corrosion, or damage on the existing sensor rod.
  • The ceramic insulator is cracked or broken.

Installation Tips

  • Disconnect electrical power to the furnace unit before servicing.
  • Avoid touching the metal rod with bare hands; handle by the ceramic base.
  • Ensure the sensor is correctly positioned in the pilot or main burner flame.
  • Confirm the mounting screw and wire are securely fastened.
Product image
Product image
Product image
  • WIDE COMPATIBILITY

    WIDE COMPATIBILITY

    Replaces Part Numbers 69W43, 69W4301, LB-74940B, LB74940B Compatible with specific Furnace of Lennox | Armstrong | Ducane
  • FIX FURNACE'S SYMPTOMS

    FIX FURNACE'S SYMPTOMS

    Short cycling | No heat or inconsistent heating | Delayed ignition | Error codes | Dirty flame sensor rod | Cracked ceramic insulator
  • EFFECTIVE SOLUTION

    EFFECTIVE SOLUTION

    Enjoy the great feeling when your furnace works properly like before - BlueStars brings DIY solutions to help you deal with any trouble
  • IMPORTANT NOTE

    IMPORTANT NOTE

    This is a replacement part designed to be compatible with certain appliances. Any brand names mentioned are used solely to indicate compatibility.
LONG-LASTING SOLUTION

LONG-LASTING SOLUTION

Made of high-grade wear-resistant Metal and Ceramics, ensuring durability and resilience against temperature changes
PRECISION FLAME DETECTION

PRECISION FLAME DETECTION

Ensure home's safety by automatically shutting off the furnace whenever no flame is detected inside, preventing gas leaks
6 SIMPLE STEPS TO INSTALL

6 SIMPLE STEPS TO INSTALL

1. Turn off furnace power, close gas valve, and remove the front panel; 2. Disconnect the wire from the old sensor; 3. Unthread the mounting screw; 4.Slide the old sensor out; 5. Install the new one, secure it into place, and reconnect wire; 6. Reattach the panel, open gas valve and turn power back on
Probe Shape
‎90° angled probe; crook on end approx. 1.31"
Rod Diameter
‎0.114"
Overall Width / Length
‎4-11/16" (4.687")
Rod Material
‎High-temperature flame rod with alumina-ceramic insulator
Rod Max Temperature
‎2190°F
Ceramic Max Temperature
‎1000°F
Insulation Max Temperature
‎250°F

FAQ

This sensor is designed for use in Lennox, Armstrong, and Ducane furnace systems. It is compatible with a wide range of units, including the EL180 and ML18UH series.
This part replaces 69W43 and cross-references with part numbers 69W4301, LB-74940B, and LB74940B.
A failing flame sensor typically causes the furnace to ignite for a few seconds and then immediately shut down. This happens because the sensor is unable to detect the flame, triggering a safety lockout to prevent gas buildup.
Installation is straightforward and generally requires only a 1/4-inch nut driver or a screwdriver to remove the mounting screw and disconnect the wire terminal. The sensor features a 3/16-inch male terminal for an easy plug-in connection.
Flame sensors fail primarily due to the buildup of carbon deposits or oxidation on the sensing rod. Over time, this insulating layer prevents the sensor from completing the electrical circuit with the flame, causing the control board to incorrectly assume the burner has not lit.
You can sometimes restore function by gently cleaning the rod with a fine-grit abrasive pad or steel wool to remove carbon buildup. However, if the ceramic insulator is cracked or the rod is heavily pitted, the sensor must be replaced to ensure safe and reliable furnace operation.