Disclosed is an electrically heated aerosol generating smoking system having a control system for measuring temperature change of a heating element compared with power input applied to the heating element to determine depletion of a liquid substrate. The electrically operated aerosol generating system (100) for receiving an aerosol - forming substrate (115) comprises a liquid storage portion (113) for storing liquid aerosol - forming substrate, an electric heater (119) comprising at least one heating element for heating the liquid aerosol - forming substrate, and electric circuitry (109) for determining depletion of liquid aerosol- forming substrate heated by the heater based on a relationship between a temperature of the heating element and power applied to the heating element.
