A capacitive detection device includes a capacitive sensor having a sense electrode and an auxiliary electrode that are arrangeable in the vicinity of an electric heater member for mutual capacitive coupling. The capacitive detection device has a signal voltage source providing an alternating measurement voltage, a complex impedance measurement circuit for measuring complex sense currents and for determining a complex impedance based on the measured complex sense current, and for electrically connecting the auxiliary electrode either with the reference voltage or with the guard signal. The method includes providing the measurement signal to the sense electrode and electrically connect the auxiliary electrode selectively either to the reference voltage or to the guard voltage; determining capacitance values in the two different connection states of the auxiliary electrode; and calculating a compensated capacitance value as a weighted sum of the two determined capacitance values, wherein the weighting factors are predefined constant values.