Siemens Flame sensor QRB4A-B110B70

The QRB4A-B110B70 is a flame sensor from Siemens, built as a photodetector. It uses photoelectric flame detection to monitor combustion in oil-fired burners that run on diesel fuel or heavy oil. The housing is made of heat-resistant plastic and mounts directly into the burner equipment, where it is used in boilers, heat generators, and similar burner devices. When the flame is present it sends a signal to the burner control; if the flame is lost it triggers an emergency fuel shut-off.

Flame sensors of this kind are chosen by detection principle (UV or IR), spectral response, response time, cable/connector type, and the mechanical mounting arrangement. Check that the replacement matches the existing sensor's mounting form, as these are often installed with a viewing tube or sleeve aimed at the flame. Before ordering, confirm whether your burner control expects a UV or IR signal, because using the wrong type prevents proper flame detection.

With sensors of this type, a contaminated window from oil or soot residue is a usual cause of weak or false signals, and an ageing sensing element can also produce a weak output. Problems show up as burner lockouts or fuel shut-off while a flame is present, or as failure to keep the fuel supply open after ignition. Inspect the sensor window for deposits, examine the cable and connector for damage, and make sure the sensor is positioned with a clear view of the flame.