The method for burning a fuel from a pre-determined fuel group originating from a connection of a burner device to a supply source, taking into account a value of a required power of the burner device, the burner device comprising at least one sensor, a signal processing unit and a monitoring unit with a memory, in which at least one error range of characteristic values is held for the pre-determined fuel group, wherein the at least one error range of characteristic values exclusively comprises those characteristic values for which the occurrence is to be avoided during the combustion of the pre-determined fuel group by the burner device, the method comprising the steps Acquiring at least one signal of the at least one sensor; Transmitting the at least one signal to the signal processing unit; Processing the at least one signal to a measured air ratio value; Transmitting the measured air ratio value to the monitoring unit; Assigning the at least one measured air ratio value and the required power of the burner device to a pair of values for the fuel comprising a value of a fuel supply to the burner device and the value of the required power of the burner device, Producing an error signal if the assigned pair of values lies outside the range for a safe presence of the fuel of the pre-determined fuel group; characterised in that the method comprises Comparing the assigned pair of values with the at least one error range of characteristic values held in the memory of the monitoring unit Detecting that the assigned pair of values lies outside a range for a safe presence of the fuel from the predetermined fuel group, if as a result of the comparison the established position of the assigned pair of values lies in the at least one error range of characteristic values held in the memory of the monitoring unit; wherein a first characteristic curve band with at least two limit curves for a first fuel group and a second characteristic curve band with at least two limit curves for a second fuel group are additionally held in the memory of the monitoring unit, the method additionally comprising the steps: Determining a limit characteristic curve (19, 21, 22) which runs between neighbouring limit curves of the first and the second characteristic curve band (17 - 18), wherein the neighbouring limit curves below the at least two limit curves of the first characteristic curve band and below the at least two limit curves of the second characteristic curve band are those limit curves that, for each given power of the burner device, have the smallest distance from one another; and Storing the limit characteristic curve (19, 21, 22) determined in the memory of the monitoring unit. Acquiring at least one signal of the at least one sensor; Transmitting the at least one signal to the signal processing unit; Processing the at least one signal to a measured air ratio value; Transmitting the measured air ratio value to the monitoring unit; Assigning the at least one measured air ratio value and the required power of the burner device to a pair of values for the fuel comprising a value of a fuel supply to the burner device and the value of the required power of the burner device, Producing an error signal if the assigned pair of values lies outside the range for a safe presence of the fuel of the pre-determined fuel group; Comparing the assigned pair of values with the at least one error range of characteristic values held in the memory of the monitoring unit Detecting that the assigned pair of values lies outside a range for a safe presence of the fuel from the predetermined fuel group, if as a result of the comparison the established position of the assigned pair of values lies in the at least one error range of characteristic values held in the memory of the monitoring unit; wherein a first characteristic curve band with at least two limit curves for a first fuel group and a second characteristic curve band with at least two limit curves for a second fuel group are additionally held in the memory of the monitoring unit, the method additionally comprising the steps: Determining a limit characteristic curve (19, 21, 22) which runs between neighbouring limit curves of the first and the second characteristic curve band (17 - 18), wherein the neighbouring limit curves below the at least two limit curves of the first characteristic curve band and below the at least two limit curves of the second characteristic curve band are those limit curves that, for each given power of the burner device, have the smallest distance from one another; and Storing the limit characteristic curve (19, 21, 22) determined in the memory of the monitoring unit. Determining a limit characteristic curve (19, 21, 22) which runs between neighbouring limit curves of the first and the second characteristic curve band (17 - 18), wherein the neighbouring limit curves below the at least two limit curves of the first characteristic curve band and below the at least two limit curves of the second characteristic curve band are those limit curves that, for each given power of the burner device, have the smallest distance from one another; and Storing the limit characteristic curve (19, 21, 22) determined in the memory of the monitoring unit.