Method of controlling an HVAC system comprising: - at least one flow regulator comprising an actuatable element for regulating fluid flow in a fluid path; - an electro-mechanical actuator associated with the flow regulator, to actuate the flow regulator, wherein the actuator comprises an electric motor driving a movable output member; - one or more sensors associated with the actuator, wherein the sensors are chosen from the group consisting of load sensors, force sensors, torque sensors, current sensors, voltage sensors, power sensors, speed sensors and position sensors; - a controller operatively connected with the actuator and the sensor(s); - optionally, a mechanism, optionally a lever mechanism, operatively connecting the output member with the flow regulator; wherein the method comprises the steps of: i. actuating the flow regulator; ii. receiving signals from the one or more sensors; iii. determining an actual or forthcoming malfunction, based on the signals received in step ii.; iv. indicating said actual or forthcoming malfunction to an operator of said HVAC system; wherein it is distinguished in step iv. between an actual or forthcoming malfunction of: - the actuator; and - the flow regulator; characterized in that the step of determining an actual or forthcoming malfunction comprises diagnosing a forthcoming malfunction. - at least one flow regulator comprising an actuatable element for regulating fluid flow in a fluid path; - an electro-mechanical actuator associated with the flow regulator, to actuate the flow regulator, wherein the actuator comprises an electric motor driving a movable output member; - one or more sensors associated with the actuator, wherein the sensors are chosen from the group consisting of load sensors, force sensors, torque sensors, current sensors, voltage sensors, power sensors, speed sensors and position sensors; - a controller operatively connected with the actuator and the sensor(s); - optionally, a mechanism, optionally a lever mechanism, operatively connecting the output member with the flow regulator; wherein the method comprises the steps of: i. actuating the flow regulator; ii. receiving signals from the one or more sensors; iii. determining an actual or forthcoming malfunction, based on the signals received in step ii.; iv. indicating said actual or forthcoming malfunction to an operator of said HVAC system; wherein it is distinguished in step iv. between an actual or forthcoming malfunction of: - the actuator; and - the flow regulator; characterized in that the step of determining an actual or forthcoming malfunction comprises diagnosing a forthcoming malfunction. wherein the method comprises the steps of: i. actuating the flow regulator; ii. receiving signals from the one or more sensors; iii. determining an actual or forthcoming malfunction, based on the signals received in step ii.; iv. indicating said actual or forthcoming malfunction to an operator of said HVAC system; i. actuating the flow regulator; ii. receiving signals from the one or more sensors; iii. determining an actual or forthcoming malfunction, based on the signals received in step ii.; iv. indicating said actual or forthcoming malfunction to an operator of said HVAC system; wherein it is distinguished in step iv. between an actual or forthcoming malfunction of: - the actuator; and - the flow regulator; - the actuator; and - the flow regulator; characterized in that the step of determining an actual or forthcoming malfunction comprises diagnosing a forthcoming malfunction.