The invention relates to a method and an installation for producing liquid helium, said installation comprising a cooling/liquefaction device comprising a working circuit that subjects a helium-enriched working fluid to a thermodynamic cycle in order to produce liquid helium, said circuit comprising at least one working fluid compression body and a plurality of heat exchangers. The installation also comprises a plurality of fluid recovery lines having respective upstream ends to be selectively connected to respective reservoirs, and a first collection line having an upstream end connected to the recovery lines and a downstream end connected to a receiving body that can supply the working circuit with a working fluid. The installation is characterized in that it comprises at least one second and one third collection line that each have an upstream end connected to the recovery lines and a downstream end connected to the working circuit, the upstream ends of the second and third collection lines being connected at separate determined positions of the working circuit, that respectively correspond to separate temperature levels of the working fluid in the working circuit.