In a duplex printer with automatic duplex printing by recirculating the sheets printed on their first sides through a duplex path for printing their second sides before feeding them to the output path, electronic information corresponding to a pre-set maximum level of acceptable sheet weight for that printer is compared to a remote user job input with electronic information corresponding to the desired sheets to be printed. If exceeded, the printer automatically switches to a different duplex printing mode in which the heavyweight sheets are printed on only one side and fed to the output path, and a GUI at the printer automatically displays instructions to unload these simplex printed sheets and properly reload them in an input in the correct orientation to print their opposite sides with locally stored page images for those opposite sides, and printing is restarted at the printer rather than the remote job input site.