Siemens Flame sensor QRB4A-B036A25

The Siemens QRB4A-B036A25 is a flame sensor / photodetector designed for monitoring flame presence in liquid fuel burners. It operates on the photoelectric principle, detecting light emission from the flame and transmitting a signal to the burner control. This model is compatible with Siemens LOA and LMO burner controls and is intended for use with diesel fuel and heavy oil. The sensor features a compact design with a heat-resistant plastic housing, facilitating easy installation directly into the burner. It provides fast response to flame loss, ensuring safe and stable operation in automatic combustion control systems.

When selecting a replacement flame sensor of this type, confirm that the electrical interface and mechanical fit match the original. Parts of this kind are chosen by detection principle, spectral range, response time, cable length, connector type, and mounting sleeve. Measure the mounting dimensions and compare the connector configuration before ordering. Ensure the sensor is compatible with the burner control model and fuel type.

Common failure modes for this type of sensor include a contaminated or fogged optical window, a weakened sensing cell that no longer delivers a stable signal, or a damaged sheath exposing internal components. When the sensor fails, the burner control may lock out and shut down fuel supply, preventing unburned fuel accumulation. Regular testing of the sensor output during servicing can identify these issues before they cause nuisance lockouts.