Abstract: The invention relates to a method and to apparatus for liquefying fuels for compression ignition engines and for heating installations, with the apparatus being designed to prevent filters becoming clogged with paraffin crystals and also to unclog such filters by projecting streamlines of very hot fuel (up to 70.degree. C.) thereon. The apparatus comprises one or more electrical heater resistances (18) of the extra flat circuit type formed on an electrically-insulating support (17) and then coated with an electrically-insulating coating, said resistances being placed in one or more chambers (1) which are of small volume relative to the volume of the filter and which are situated immediately upstream from the filter elements. The apparatus is such that the fuel follows an approximately U-shaped path around the heater element. An electrical temperature sensor (19) is immersed in the flow of fuel. This sensor is a low current sensor and its resistance varies as a function of temperature.