Disclosed is a method and a device for detecting a non-condensable portion of a medium, which has at least one condensable portion and is present at least partially in gaseous form, wherein in a first method step a temperature measuring device measures a temperature of the medium and a pressure measuring device measures a pressure of the medium, wherein in a second method step a ratio of the pressure to temperature is formed by means of an electronic measuring/operating circuit and this ratio is compared with a desired ratio of a desired pressure and a desired temperature, and wherein in a third method step the electronic measuring/operating circuit outputs a report in case of a minimum deviation of the ratio from the desired ratio.