Siemens Outdoor NTC sensor QAC34/101

This product is the Siemens outdoor NTC temperature sensor QAC34/101, belonging to the temperature sensor category. It operates on the NTC principle, providing accurate ambient temperature measurement. Its robust housing suits outdoor installation. It is designed to feed the outside air temperature to a control system, enabling weather-compensated heating control and frost protection.

Outdoor NTC sensors of this kind are selected by matching the resistance characteristic to the control board's input, typically 10 or 12 kΩ at 25 °C. The cable length, connector type (if any), and housing protection rating must also suit the installation. Mount the sensor on an external wall, preferably north-facing and away from direct sunlight or heat sources. Before ordering, compare the new part's resistance curve with the original to ensure correct compensation.

Common failure modes of this kind include a drifting NTC characteristic, causing the boiler to modulate incorrectly, and a broken cable or poor connection that interrupts the signal. When the sensor fails, the controller may read an impossible outside temperature, resulting in erroneous weather-compensated control or loss of frost protection. Check the wiring, connectors, and the sensor body for damage before suspecting the control board.