The invention relates to a filter, especially a filter for lubricating oil in an internal combustion engine, comprising an inlet for the crude liquid and an outlet for the purified liquid. A filter insert (12) is arranged inside said filter, in addition to a valve, especially a pressure control valve (23), whereby parts of the pressure control valve (23) are provided with coatings, especially teflon or silicon coatings. The inventive heater can also contain a heating element (34) in the region of said valve.