A method for controlling a fluid flow through a valve arranged in a fluid flow system , the valve comprising a valve seat and a valve element , the valve element being movable with respect to the valve seat , an opening degree of the valve being determined by a relative position between the valve seat and the valve element , the fluid flow system further having a flow sensor arranged therein, the method comprising the steps of: - measuring a flow rate, Q M , by means of the flow sensor , the measured flow rate Q M being measured at a corresponding opening degree, φ M , of the valve ; - comparing the measured flow rate, Q M , and a predetermined flow rate threshold value, Q T , below which the flow sensor operates in an unreliable measurement region; - in the case that Q M <Q T , performing a calibration of the flow sensor ; characterized in that the calibration of the flow sensor is performed by performing the steps of: increasing the opening degree of the valve while measuring the flow rate by means of the flow sensor , until the flow rate, Q M , measured by the flow sensor , is at least equal to Q T , establishing a relationship between actual flow rate and opening degree of the valve , based on the measurements of the flow rate during increase of the opening degree and while the flow rate, Q M , is above Q T , and determining a correction, C, based on the established relationship; and in that the method further comprises the steps of: - after the calibration step, setting the opening degree of the valve back to an operational opening degree, φ A , the operational opening degree, φ A , resulting in a flow rate below the threshold value, Q T , and - subsequently controlling the opening degree of the valve on the basis of flow rate measurements performed by means of the flow sensor , corrected by the correction, while the measured flow rate is below the threshold value, Q T . - measuring a flow rate, Q M , by means of the flow sensor , the measured flow rate Q M being measured at a corresponding opening degree, φ M , of the valve ; - comparing the measured flow rate, Q M , and a predetermined flow rate threshold value, Q T , below which the flow sensor operates in an unreliable measurement region; - in the case that Q M <Q T , performing a calibration of the flow sensor ; increasing the opening degree of the valve while measuring the flow rate by means of the flow sensor , until the flow rate, Q M , measured by the flow sensor , is at least equal to Q T , establishing a relationship between actual flow rate and opening degree of the valve , based on the measurements of the flow rate during increase of the opening degree and while the flow rate, Q M , is above Q T , and determining a correction, C, based on the established relationship; - after the calibration step, setting the opening degree of the valve back to an operational opening degree, φ A , the operational opening degree, φ A , resulting in a flow rate below the threshold value, Q T , and - subsequently controlling the opening degree of the valve on the basis of flow rate measurements performed by means of the flow sensor , corrected by the correction, while the measured flow rate is below the threshold value, Q T . <EOS>