Do you have low or no suction in the upstairs valves of your central or built in vacuum? You may have clogged pipes. If pipes are run in the attic and above the insulation condensation can build up inside the pipes from the fluctuation between hot and cold air temperature. This will cause dirt to build up gradually over time. The best resolution is to re-pipe the clogged section and either run it below the insulation or insulate the new piping itself. See below pictures.