The present invention concerns a process for the synthesis of hydrocarbons from a feed comprising synthesis gas, in which a solid catalyst comprising cobalt is used in a three-phase reaction section operated such that said catalyst is maintained in suspension in a liquid phase by movement of a gas phase from the bottom to the top of said reaction section, said process comprising an external loop for separating waxes, characterized in that: 1) the theoretical ratio PH2O:PH2 in the external loop for separating waxes is determined using the following calculation: PH2O:PH2 theoretical=Cv/(R1−Rft×Cv) where Cv=(COinlet−COdegas)/COinlet R1=H2 inlet/COinlet Rft=(H2 inlet−H2 degas)/(COinlet−COdegas) 2) if the theoretical ratio PH2O:PH2 determined in step 1) has a value of Rthreshold or higher, the temperature in the degassing means for the external loop for separating waxes is reduced, 3) steps 1) to 2) are repeated until the theoretical ratio PH2O:PH2 has a value strictly less than Rthreshold, where Rthreshold is in the range 0.1 to 1.1.