A method for operating a converter for the energy conversion of fuel from at least one main fuel supply, and from at least one auxiliary fuel supply for operating the converter directly and/or by operating an auxiliary unit, comprises: detecting the amount of fuel in the main fuel supply; detecting the amount of fuel in the auxiliary fuel supply, at least with respect to a predetermined minimum amount; in response to the minimum amount being reached, generating a signal that blocks at least one of a) filling of the main fuel supply, and b) startup of the converter via a control unit; and deactivating the blocking in response to the auxiliary fuel supply being replenished.