The Siemens STA161.65L10 (S55174-A214) is a high-performance electrothermal modulating actuator designed for precise control of radiator and small zone valves. Operating on AC 24 V with a DC 0…10 V control signal, it ensures smooth modulation of valve position for energy-efficient heating and cooling applications. With a 6.5 mm stroke and spring return mechanism, the actuator guarantees safe, reliable operation, automatically returning the valve to the closed position when de-energized. Featuring position indication and Siemens’ “first-open” automatic valve stroke detection for easy commissioning, this actuator is ideal for both new installations and retrofit projects across residential, commercial, and light-industrial systems.