The zone valves are closed when de-energized. An On/Off controller (thermostat) is required to drive the motorized valve actuators. If the medium temperature deviates from the setpoint, the controller sends a control signal to the actuator to open the valve. When the medium temperature returns to the setpoint, the control signal is cut off and the valve closes.
2-position SPST control signal
The actuator requires an On/Off controller, typically a room thermostat.