Oxidized iron can be plugging up the inside of the valve and/or the outlet manifold in the filter tank. If the venturi for air injection is in-line by the well tank this may be where the restriction is. Often oxidized iron will build up in the line between the well tank and filter system plugging it up. Bypass the whole system to see if there is water pressure in the house. This type fitration system should backwash every day, 2 10 minute backwash cycles are sufficient.
RJ