An electrically operated aerosol-generating system comprising: an electric heater (119, 201) comprising at least one heating element for heating an aerosol-forming substrate (115, 210); a power supply (107, 207); and electric circuitry (109, 209) connected to the electric heater (119, 201) and to the power supply (107, 207) and comprising a memory, the electric circuitry (109, 209) being configured to: measure an initial electrical resistance (Ri) of the electric heater (119, 201); measure a subsequent electrical resistance of the electrical heater (119, 201) after the measurement of the initial electrical resistance (Ri); determine the difference (ΔR) between the initial electrical resistance (Ri) and the subsequent electrical resistance; determine an adverse condition when the determined difference (ΔR) between the subsequent electrical resistance and the initial electrical resistance (Ri) is greater than a maximum threshold value (ΔR max) or is less than a minimum threshold value (ΔR min) stored in the memory; control power supplied to the electric heater (119, 201) based on whether there is determined to be an adverse condition or provide an indication if there is determined to be an adverse condition; store the determination of an adverse condition in the memory; determine the number of consecutive determinations of adverse conditions based on the stored determinations of adverse conditions; and disable the electric heater (119, 201) or permanently or irreversibly prevent or inhibit the supply of power to the at least one heating element if the determined number of consecutive determinations of adverse conditions is greater than a maximum threshold value. an electric heater (119, 201) comprising at least one heating element for heating an aerosol-forming substrate (115, 210); a power supply (107, 207); and electric circuitry (109, 209) connected to the electric heater (119, 201) and to the power supply (107, 207) and comprising a memory, the electric circuitry (109, 209) being configured to: measure an initial electrical resistance (Ri) of the electric heater (119, 201); measure a subsequent electrical resistance of the electrical heater (119, 201) after the measurement of the initial electrical resistance (Ri); determine the difference (ΔR) between the initial electrical resistance (Ri) and the subsequent electrical resistance; determine an adverse condition when the determined difference (ΔR) between the subsequent electrical resistance and the initial electrical resistance (Ri) is greater than a maximum threshold value (ΔR max) or is less than a minimum threshold value (ΔR min) stored in the memory; control power supplied to the electric heater (119, 201) based on whether there is determined to be an adverse condition or provide an indication if there is determined to be an adverse condition; store the determination of an adverse condition in the memory; determine the number of consecutive determinations of adverse conditions based on the stored determinations of adverse conditions; and disable the electric heater (119, 201) or permanently or irreversibly prevent or inhibit the supply of power to the at least one heating element if the determined number of consecutive determinations of adverse conditions is greater than a maximum threshold value. measure an initial electrical resistance (Ri) of the electric heater (119, 201); measure a subsequent electrical resistance of the electrical heater (119, 201) after the measurement of the initial electrical resistance (Ri); determine the difference (ΔR) between the initial electrical resistance (Ri) and the subsequent electrical resistance; determine an adverse condition when the determined difference (ΔR) between the subsequent electrical resistance and the initial electrical resistance (Ri) is greater than a maximum threshold value (ΔR max) or is less than a minimum threshold value (ΔR min) stored in the memory; control power supplied to the electric heater (119, 201) based on whether there is determined to be an adverse condition or provide an indication if there is determined to be an adverse condition; store the determination of an adverse condition in the memory; determine the number of consecutive determinations of adverse conditions based on the stored determinations of adverse conditions; and disable the electric heater (119, 201) or permanently or irreversibly prevent or inhibit the supply of power to the at least one heating element if the determined number of consecutive determinations of adverse conditions is greater than a maximum threshold value.