Siemens Flame sensor QRB1A-A150B70A

The Siemens QRB1A-A150B70A is a compact flame sensor with a heat-resistant plastic housing, intended for photoelectric flame monitoring in oil burners burning diesel or heavy oil. It detects the light emitted by the flame and sends a signal to the burner control. The sensor is designed for built-in mounting in the burner and is suitable for automatic combustion control systems, including Siemens LOA and LMO controls. Its high sensitivity and fast response to flame loss enable immediate fuel cutoff in the event of flame failure.

When replacing a flame sensor of this type, ensure the detection principle and spectral range match the original and the fuel. Verify the response time, cable length, connector type, and mounting sleeve diameter, as these vary between models. The sensor must have a direct line of sight to the luminous flame, and the mounting position inside the burner must be compatible. Confirm that the sensor is compatible with the burner control series before ordering.

If a flame sensor of this kind fails, the burner control receives no or an insufficient flame signal, so it will not keep the fuel valves open and will enter lockout, often during start-up. Typical failure modes are a dirty or contaminated optical window, an ageing sensor cell producing a weak signal, or a damaged outer sheath. Check the sensor window for fouling, inspect the cable and sheath for breaks, and compare the sensor output with the expected values while the flame is present.