A method of controlling a heat generating device comprising a first heat generator, a second heat generator, and a heat accumulator for storing heat, wherein said second heat generator is configured to supply heat to said heat accumulator, and wherein said first heat generator is able to enter at least two operating modes and, in a first operating mode of said at least two operating modes, supplies heat to said heat accumulator and, in a second operating mode of said at least two operating modes, does not supply heat to said heat accumulator, the method for controlling said heat generating device comprising the steps of: - obtaining at least one accumulator temperature actual value T IST based on a temperature of at least a portion of said heat accumulator, - determining, whether said first heat generator is in the first operating mode, - supplying heat to said heat accumulator by said first heat generator when it is determined that said first heat generator is in the first operating mode of said at least two operating modes, - setting an accumulator temperature target value T SOLL indicating a target value of the accumulator temperature in said heat accumulator, - comparing the set accumulator temperature target value T SOLL with the obtained accumulator temperature actual value T IST for determining a deviation parameter between said accumulator temperature target value T SOLL and said accumulator temperature actual value T IST, - determining, by means of the determined deviation parameter, whether heat is to be supplied to said heat accumulator by said second heat generator, wherein, in a first operating mode of said heat generating device, heat is to be supplied to said heat accumulator by said second heat generator if the determined deviation parameter meets a first condition, characterized by the further step of: - switching an operating mode of said heat generating device from the first operating mode to the second operating mode based on a supply of heat by said first heat generator in the first operating mode, wherein, in the second operating mode of said heat generating device in the step of determining, whether heat is to be supplied to said heat accumulator by said second heat generator, it is determined that heat does not have to be supplied to said heat accumulator by said second heat generator. - obtaining at least one accumulator temperature actual value T IST based on a temperature of at least a portion of said heat accumulator, - determining, whether said first heat generator is in the first operating mode, - supplying heat to said heat accumulator by said first heat generator when it is determined that said first heat generator is in the first operating mode of said at least two operating modes, - setting an accumulator temperature target value T SOLL indicating a target value of the accumulator temperature in said heat accumulator, - comparing the set accumulator temperature target value T SOLL with the obtained accumulator temperature actual value T IST for determining a deviation parameter between said accumulator temperature target value T SOLL and said accumulator temperature actual value T IST, - determining, by means of the determined deviation parameter, whether heat is to be supplied to said heat accumulator by said second heat generator, wherein, in a first operating mode of said heat generating device, heat is to be supplied to said heat accumulator by said second heat generator if the determined deviation parameter meets a first condition, - switching an operating mode of said heat generating device from the first operating mode to the second operating mode based on a supply of heat by said first heat generator in the first operating mode,