The Main Boiler is the cooling system of the Biologic Space Laboratories research station. During the events of Metroid Fusion, Samus Aran discovered the X Parasite's plot to overheat the cooling system and thus destroy the station, destroying themselves but giving the X on SR388 a chance to survive. Initially, it was believed that the SA-X, Samus' X-mimic, was responsible, but it was later discovered to be a human scientist infected by the X.