The throttling of the main steam governor valves, which can be quickly opened when required, has prevailed as the most frequent procedure for rapid output variation. The prerequisite for the effectiveness of this measure is, however, sufficiently large storage in the boiler. Since this prerequisite is not often fulfilled, it is possible that output cannot be continuously increased, because the storage is exhausted before the firming rate becomes effective. The activation of other forms of storage, which can be used in the feed water or condensate zones, should therefore be available in addition.