A sensor for detecting bubbles in gas phase present in a liquid flowing through a flow path. The sensor can include a heating element for heating the liquid, which can be provided with a predetermined level of power at least during detecting, and a transducer arrangement arranged for generating a measurement signal indicative for the temperature of the heating element. The sensor furthermore can include a comparator arrangement for comparing a measurement value of the measurement signal with a predetermined threshold level, which can correspond to a reference temperature attainable by the heating element in response to the predetermined level of power and a minimum velocity attainable by the liquid in the flow path. Based on the latter comparison, the comparator arrangement can generate an output signal indicative for a possible presence of bubbles in gas phase.