Results of testing a novel process of startup of 800-MW supercritical-pressure units at sliding pressure in the entire conduit of the once-through boiler with the temperature of extraneous steam in the station-service header supplying the turbine-feeding pump reduced to ∼250°C and intermediate transfer of its feed to its own steam through the available station-service starting-shedding device are given. It is shown that the use of this process makes it possible to fully pass to steam supply of the unit from the colder second extraction of the turbine. A variant of updating the steam feeding circuit is suggested.