the present invention relates to electrically heated steam generators and means for preventing and removing incrustations due to hard water in such generators . according to the invention this is achieved by means of a superimposed direct current the polarity of which is periodically changed whereby gas bubbles , mainly carbon dioxide and hydrogen , are generated at the electrodes causing segregation and removing of incrustations on the electrodes , the method and means for feeding of the superimposed direct current being variable .