The present invention relates to a method for regulating a closed intermediate medium circuit when heat exchanging a primary medium within a heat exchanger (B) fed by means of a pump (Al) so as to be evaporated or condensed therein, the closed circuit is passing through the heat exchanger (B) and is comprising a tank (H) and pump (E) for condensed intermediate medium and at least one heat exchanger (Gl, G2) evaporising or condensing intermediate medium to be passed through the heat exchanger (B) for primary medium, wherein controlling flow of intermediate medium in the closed circuit as function of primary medium through the heat exchanger (B).