Furnace burners light but shut off after a few seconds; this repeats several times before lockout.

Safety: Turn off power and gas before removing the flame sensor.

Steps:

• Locate and remove flame sensor: It is a small metal rod in front of one burner with a single wire attached.
• Clean sensor: Gently rub the rod with fine steel wool or emery cloth until shiny. Do not sand aggressively or bend the rod.
• Reinstall and tighten: Reinstall the sensor, ensuring it is fully inserted into the flame path and the mounting screw is tight.
• Check ground: Verify that the burner rack and control board ground wires are secure.

If the problem persists after cleaning, the control board or wiring may need professional diagnosis.