Disclosed is a method for controlling a heating device comprising a PTC heating resistor, wherein a pulse width modulated voltage is applied to the PTC heating resistor, said pulse width modulation having a first time period. The voltage is switched off for a second time period that is at least a hundred times larger than the first period, if a condition A or a condition B are fulfilled, wherein condition A requires that power is below a power threshold and a gradient of power is below a power gradient threshold, and wherein condition B requires that electrical resistance is above a resistance threshold for a third time period that is larger than the first time period, but smaller than the second time period.