Siemens Flame sensor QRB4A-B050B70A

The Siemens QRB4A-B050B70A is a flame sensor (photodetector) designed for monitoring flame presence in oil burners using diesel or fuel oil. It operates on a photoelectric principle, detecting light emission from the flame and transmitting a signal to the burner control unit. This sensor is integrated into the burner and is compatible with Siemens LOA and LMO series controls. It features a compact design, high sensitivity, and fast response to flame loss, ensuring safe and stable operation in automatic combustion control systems. The housing is made of heat-resistant plastic, and the device is resistant to operational loads.

When selecting a replacement flame sensor of this type, confirm that the detection principle (photoelectric) and spectral range match the burner's fuel and flame characteristics. Check the sensor's electrical ratings (voltage and current) for compatibility with the burner control's output circuit. Ensure the mounting sleeve diameter and cable length/connector type are suitable for the existing installation. The sensor must have a direct line of sight to the flame, so verify its position and alignment during installation.

Typical failure modes for this kind of sensor include a contaminated lens (soot or oil residues), an aged photocell producing a weak signal, or a broken outer sheath allowing moisture ingress. When the sensor fails, the burner control may not receive a valid flame signal within the programmed safety time, leading to a lockout and fuel supply shutdown. Check the sensor's optical window for cleanliness and ensure it is properly aligned with the flame.