A method for the deaeration of a liquid circuit, wherein the deaeration occurs by establishing a reduced pressure in said circuit for rarefying air or other gases present therein, by producing a saturated vapor at a pressure which is higher than the reduced pressure but lower than the atmospheric pressure and maintaining a current of said vapor through said circuit for expelling said rarefied air or other gases therefrom, and thereafter pumping a deaerated liquid through the circuit for expelling the vapor therefrom.