check that your pump is working as the upstairs radiators may work on gravity thus still heating, but the downstairs need circulation. If the pump is working, try closing some radiators off upstairs and if downstairs start to work the system may need balanced. To balance, the radiator closest to the boiler does not need to be open as fully as the next closest, and so on, and so on. The balancing is done using the return valve on each rad. It could also be an airlock, but closing the rads upstairs could move the airlock also. Hope this helps.
rimrex, March 2010
