<p>An appliance heater (2) has a temperature sensor (14) to provide a sensor signal T read. A controller (15) responsive to the sensor signal controls power supplied to the heater so as to maintain it at an operating temperature within a working temperature range for normal user operation. The controller is also operable to detect a sensor malfunction by comparing the sensor signal (T read) with data corresponding to upper and lower limits (T work_max, T work_min) of the working temperature range for the normal user operation and to disable further normal user operation for the heater in the event that the temperature indicated by the sensor signal falls outside of the working temperature range.</p>
