The Rheem 62-23543-01 Flame Sensor is a small but critical safety component used in gas‐fired furnaces (such as those from Rheem, Ruud, WeatherKing, etc.). It is designed to detect the presence of a burner flame and communicate that to the furnace’s control board. If the flame is properly established, the sensor signals the control board to continue normal operation (for example, stop the igniter once the flame is stable). If the flame is not detected, the sensor helps trigger a safety lock‐out, preventing unsafe conditions.