A printer comprising: - a conveyer arranged to convey print media sheets (1 - 9) one after another in a conveying direction (X); - a print head disposed at the conveyer and having an array of dot printing elements, the array extending in a direction Z normal to the conveying direction, the print head being arranged to print images onto the media sheets (1 - 9) in accordance with actuation instructions sent to the print head; and - a maintenance manager adapted to analyze the actuation instructions and to decide on a maintenance operation for the print head on the basis of the actuation instructions , and - a controller adapted to convert print instructions that specify images to be printed onto the media sheets (1 - 9) into the actuation instructions for the print head , - wherein the conveyer is arranged to convey sheets (1 - 9) with different formats which differ in their dimension in the direction Z, and the maintenance manager is adapted to decide on the maintenance operation, whenever the format of the sheets to be conveyed to the print head changes from a narrower format to a wider format with a dimension in Z direction larger than that of the narrower format, on the basis of actuation instructions for printing elements located within the width range (w2) of the wider format but outside of the width range (w1) of the narrower format, characterized in that the maintenance manager is adapted to decide on a maintenance operation on the basis of whether or not the actuation instructions for the dot printing elements located outside of the width range (w1) of the narrow format but inside the width range (w2) of the wider format specify that at least one of these dot printing elements is needed for printing a part of the image. - a conveyer arranged to convey print media sheets (1 - 9) one after another in a conveying direction (X); - a print head disposed at the conveyer and having an array of dot printing elements, the array extending in a direction Z normal to the conveying direction, the print head being arranged to print images onto the media sheets (1 - 9) in accordance with actuation instructions sent to the print head; and - a maintenance manager adapted to analyze the actuation instructions and to decide on a maintenance operation for the print head on the basis of the actuation instructions , and - a controller adapted to convert print instructions that specify images to be printed onto the media sheets (1 - 9) into the actuation instructions for the print head , - wherein the conveyer is arranged to convey sheets (1 - 9) with different formats which differ in their dimension in the direction Z, and the maintenance manager is adapted to decide on the maintenance operation, whenever the format of the sheets to be conveyed to the print head changes from a narrower format to a wider format with a dimension in Z direction larger than that of the narrower format, on the basis of actuation instructions for printing elements located within the width range (w2) of the wider format but outside of the width range (w1) of the narrower format, characterized in that the maintenance manager is adapted to decide on a maintenance operation on the basis of whether or not the actuation instructions for the dot printing elements located outside of the width range (w1) of the narrow format but inside the width range (w2) of the wider format specify that at least one of these dot printing elements is needed for printing a part of the image. <EOS>