An electrically operated aerosol-generating system comprising: a heating element for heating an aerosol-forming substrate; a power supply for supplying power to the heating element; a temperature sensor for sensing a temperature at the heating element; and electric circuitry in communication with the heating element, the sensor and the power supply, the electric circuitry comprising a memory and being configured to: regulate the supply of power to the heating element based on the measured temperature from the temperature sensor; determine an adverse condition when a reduction in power supplied to the heating element required to reach or maintain a predetermined temperature over successive heating cycles falls outside a predefined range, by comparing the minimum power supplied to the heating element in a given heating cycle with that supplied in one or more preceding heating cycles, said predefined range being stored in the memory; and control power supplied to the heating element based on whether there is an adverse condition or provide an indication when there is an adverse condition; wherein the system comprises a device and a removable cartridge, wherein the power supply and the electric circuitry are in the device and the heating element is in the removable cartridge, and wherein the cartridge comprises a liquid aerosol-forming substrate. a heating element for heating an aerosol-forming substrate; a power supply for supplying power to the heating element; a temperature sensor for sensing a temperature at the heating element; and electric circuitry in communication with the heating element, the sensor and the power supply, the electric circuitry comprising a memory and being configured to: regulate the supply of power to the heating element based on the measured temperature from the temperature sensor; determine an adverse condition when a reduction in power supplied to the heating element required to reach or maintain a predetermined temperature over successive heating cycles falls outside a predefined range, by comparing the minimum power supplied to the heating element in a given heating cycle with that supplied in one or more preceding heating cycles, said predefined range being stored in the memory; and control power supplied to the heating element based on whether there is an adverse condition or provide an indication when there is an adverse condition; wherein the system comprises a device and a removable cartridge, wherein the power supply and the electric circuitry are in the device and the heating element is in the removable cartridge, and wherein the cartridge comprises a liquid aerosol-forming substrate. regulate the supply of power to the heating element based on the measured temperature from the temperature sensor; determine an adverse condition when a reduction in power supplied to the heating element required to reach or maintain a predetermined temperature over successive heating cycles falls outside a predefined range, by comparing the minimum power supplied to the heating element in a given heating cycle with that supplied in one or more preceding heating cycles, said predefined range being stored in the memory; and control power supplied to the heating element based on whether there is an adverse condition or provide an indication when there is an adverse condition; wherein the system comprises a device and a removable cartridge, wherein the power supply and the electric circuitry are in the device and the heating element is in the removable cartridge, and wherein the cartridge comprises a liquid aerosol-forming substrate.