A method of generating a control signal for a temperature control system is disclosed. The control signal has one of an “on” state in which the temperature control system is to be activated and an “off” state in which the temperature control system is to be deactivated. The method comprises calculating a temperature error measure in dependence on a target temperature and a current temperature value. A rate of temperature change in the environment is determined and used to set a variable error threshold. The method switches between a continuous “on” signal mode and a pulse-width-modulation (PWM) mode, in which the output signal comprises alternating “off” and “on” periods in accordance with a PWM pattern. The switch occurs in dependence on the temperature error measure and the variable error threshold.