A.O. Smith 100074673 Flame Sensor

How the Flame Sensor Works

A flame sensor sits directly in the path of the burner flame. When the burners ignite, the sensor detects the flame and sends a confirmation signal back to the control system.

Without this confirmation, the system assumes the gas failed to ignite. To protect the home, the controls quickly cut the flow of gas to the burner assembly.

Sensor Dimensions and Specifications

When matching your old part, verify that its physical measurements align with the listed dimensions for part number 100074673.

Physical measurements for this part include:

• Height: 4.15 in / 10.54 cm
• Length: 18.35 in / 46.61 cm
• Width: 10.45 in / 26.54 cm

Recognizing Failure and Replacing Safely

If the burners light and then go out after 3 to 10 seconds, a dirty flame sensor is a common cause. A light cleaning fixes many sensors. However, you should replace the part if the metal rod is bent or worn, or if the white porcelain insulator is cracked.

Follow these steps to safely inspect or swap the sensor:

1. Turn off electrical power at the breaker and shut off the gas supply valve.
2. Take a photo of every wire connected to the sensor assembly for reference.
3. Disconnect the wire terminal and remove the mounting screws holding the bracket in place.
4. Inspect the porcelain for cracks and the rod for wear or bending.
5. Install the matching sensor into position using the existing mounting bracket and screw holes.
6. Move the wire connector to the same terminal style on the replacement part.
7. Restore the gas supply and electrical power, then observe the burner cycle.

Read your old part

1. Locate the part number stamped on the metal bracket or printed on the label of your old sensor.
2. Confirm the part number reads 100074673.
3. Check that the rod length is about the same as your old one.
4. Ensure the mounting bracket and screw spacing match your existing burner assembly.
5. Verify that the electrical connector uses the same terminal style.