The tail sweep on my 280 does not move from side to side, it just drags straight behind the unit. The cleaner moves along the bottom, climbs the wall, etc. There is no blockage in the cleaner, hoses, or back-up valve. There is no pressure loss at the wall fitting or releif valve. The tail sweep adjustment screw is turned counter-clockwise about as far as it will go without falling out. The pump strainer basket is clean. The cartridge filters are clean. I have added no additional weights to the tail. What am I missing? Any help is greatly appreciated.