Siemens Flame sensor QRB4B-B025B40B

This photoelectric flame sensor is designed for flame monitoring in oil-fired burner equipment burning diesel fuel or heavy oil. It is built into automatic combustion control systems and housed in a heat-resistant plastic body with a compact design. During burner operation it detects the flame light and sends a signal to the control; if the flame is lost, it immediately triggers an emergency shutdown of the fuel supply. It provides accurate flame-presence monitoring with high sensitivity and fast response, making it suitable for boilers, heat generators, and other burner devices. Installation and simple maintenance are supported by the built-in mounting arrangement.

Flame sensors of this kind are selected by their detection principle (UV or IR), the spectral range they respond to, response time, and cable length and connector type; these must match the burner control and mounting sleeve. The sensor normally looks through a sight tube or mounting sleeve at the flame, so verify the sleeve bore and the form of the existing mounting before ordering. When replacing one, confirm that the connection arrangement is the same and that the viewing window is clean and unobstructed. If an old sensor is present, compare its connection and mounting details to ensure a direct swap without modifications.

Usual failure modes for this kind of photodetector are a contaminated or fogged viewing window, an aged sensing cell that yields a weakened signal, and a broken or damaged sheath. The burner may then fail to detect the flame, shut down intermittently, or enter lockout after the safety time when no flame is confirmed. Check the viewing window for deposits or fogging first, and inspect the connected cable or sheath before deciding that the sensor itself needs replacement.