A capacitive liquid level sensor comprising: a capacitive probe (200a-200c) having a capacitance and comprising a sensing tip wherein the capacitive probe is configured such that the capacitance of the probe changes when the sensing tip is exposed to liquid; a signal generator operable to supply an electrical signal alternating between a high and low state to the capacitive probe the electrical signal being configured such that the probe is alternately charged and discharged when the signal is high or low respectively; a comparator operable to detect the magnitude of an electrical signal across the capacitive probe and provide a first output signal value when the detected signal magnitude is greater than a predetermined threshold value and a second output signal value when the signal magnitude is less than the threshold value; a timer operable to receive an output signal from the comparator and to measure a time period starting when the comparator output signal transitions to the first output signal value and ending when the comparator output signal transitions to the second output signal value; and liquid detection means operable to utilise the time period measured by the timer to determine if the sensing tip is exposed to liquid, characterized in that said liquid detection means is adapted to determine whether the sensing tip is exposed to liquid based on whether the time period measured by the timer is greater or less than a reference value, and in that the sensor further comprises reference value auto-calibration means operable to: calculate an auto-calibration value equal to an average of a plurality of average time periods calculated by time period averaging means; determine whether the auto-calibration value is equal to the reference value; and replace the reference value with the auto-calibration value if it is determined that they are not equal. a capacitive probe (200a-200c) having a capacitance and comprising a sensing tip wherein the capacitive probe is configured such that the capacitance of the probe changes when the sensing tip is exposed to liquid; a signal generator operable to supply an electrical signal alternating between a high and low state to the capacitive probe the electrical signal being configured such that the probe is alternately charged and discharged when the signal is high or low respectively; a comparator operable to detect the magnitude of an electrical signal across the capacitive probe and provide a first output signal value when the detected signal magnitude is greater than a predetermined threshold value and a second output signal value when the signal magnitude is less than the threshold value; a timer operable to receive an output signal from the comparator and to measure a time period starting when the comparator output signal transitions to the first output signal value and ending when the comparator output signal transitions to the second output signal value; and liquid detection means operable to utilise the time period measured by the timer to determine if the sensing tip is exposed to liquid, characterized in that said liquid detection means is adapted to determine whether the sensing tip is exposed to liquid based on whether the time period measured by the timer is greater or less than a reference value, and in that the sensor further comprises reference value auto-calibration means operable to: calculate an auto-calibration value equal to an average of a plurality of average time periods calculated by time period averaging means; determine whether the auto-calibration value is equal to the reference value; and replace the reference value with the auto-calibration value if it is determined that they are not equal.