A method of modifying a quantity of air supplied for regeneration

A method for regenerating a filter device (30), comprising the steps of: Generating an exhaust gas stream to a power source (12); Supplying air to a combustion device (28) which is designed for heating the exhaust gas stream; Determining whether a parameter is above a threshold, wherein the parameter indicative of a power supplied to the combustor air amount; and Modifying an operating condition of the power source, if the parameter is above the threshold, wherein the modifying of the operating condition affecting the parameters.