Siemens Pressure switch sensor QPL25.500

This pressure switch sensor monitors differential or overpressure of air, flue gas, and other non-aggressive gases. It is designed for ventilation, boiler, burner, and HVAC systems as part of Siemens automation equipment. The housing is made of industrial heat-resistant plastic, and the unit can be wall-mounted or built in. It operates on the differential/overpressure monitoring principle.

Pressure switches of this class are selected by matching the monitored medium (air or gas), switching range and differential, connection type (thread or hose spigot), contact rating, and applicable approval class. Mounting may be wall-mounted or built-in, depending on the enclosure. Before ordering a replacement, verify that the new unit’s setpoint range and connection match the original, and inspect the impulse line for blockages.

Typical failures of this type include a torn diaphragm, a blocked impulse tube, or a drifted setpoint. These often cause burner lockouts that can be misinterpreted as ignition faults. Check the impulse line for obstructions and verify the setpoint against the actual pressure.