Siemens Flame sensor QRB3

The Siemens QRB3 is a photodetector flame sensor designed for oil-fired and industrial burners. It monitors flame presence and sends an output signal to the burner control. This device is suited to diesel and heavy oil fuels and requires direct line of sight to the flame. It features fast response to flame loss, compact design, and compatibility with Siemens burner controls.

Flame sensors of this class are selected by matching the detection principle (ultraviolet or infrared), spectral response, response time, cable length, connector type, and mounting sleeve dimensions to the burner and control input. They are usually mounted in a sleeve with the sensor window aimed at the flame, and the optical path must be unobstructed. Before ordering, measure the sleeve length and thread, and compare the existing sensor's connector and output characteristics with the replacement. After fitting, ensure the sensor is aligned and tightly seated.

Common failure modes include a contaminated or hazed window that reduces sensitivity, an aged detection cell producing a weakened signal, and a broken sheath exposing the internals to heat or moisture. When a sensor of this type stops proving flame, the burner control may lock out during ignition after the safety time. Check the old sensor for sooting or cracking, clean the mounting sleeve, and verify alignment and seating. If the problem persists, inspect the control unit settings, ignition spark, and fuel supply.