Siemens Flame sensor QRB4A-B150B70A

The Siemens QRB4A-B150B70A is a flame sensor (photodetector) designed for monitoring flame presence in liquid fuel burners, specifically for diesel fuel and heavy oil. It operates on a photoelectric detection principle and features a compact design with a heat-resistant plastic housing. The sensor is integrated into burner equipment and is compatible with Siemens LOA and LMO burner controls, as well as similar models. It provides fast response to flame loss, ensuring safe and stable operation of heating boilers and heat generators.

When selecting a flame sensor of this type, ensure the detection principle (photoelectric) and spectral sensitivity match the original, as using the wrong principle can cause failure to detect the flame or spurious detection. Check the cable length and connector configuration to match existing wiring. The sensor must be positioned so it has a direct line of sight to the flame; correct alignment and clean optics are essential, as misalignment or contamination can cause false lockouts. No adjustment is normally required beyond proper positioning.

Common failure modes for this kind of sensor include weakened signal output due to aging, leading to intermittent lockouts. Optical contamination or misalignment can also cause false lockouts, where the burner control fails to detect the flame within the safety time and initiates a shutdown. If the equipment exhibits repeated lockouts, check the sensor's optics for dirt or damage and verify its alignment with the flame.