Debris

• The bottom spray arm can get clogged from debris or residue that falls down from the racks, catching on the arm. In addition, if labels are left on items and get wet, the labels can slip down and land on the arm, creating a clog. Look at the spray arm for items or dried residue that might be causing the problem and clean as needed.
  
  

Mineral Scale

• Mineral scale buildup can occur in any area with hard water and can affect the spray arms in the dishwasher as well. If the scale builds up over the spray jets on the arm, the water spray will be reduced, lessening cleaning effectiveness. Wet a clean cloth with vinegar and use the cloth to clean the arms as needed to wipe away any mineral scale or debris.
  
  

Impeller

• The impeller, which is located inside the bottom spray arm, can also get clogged with debris. To find the impeller, disconnect power to the dishwasher, take out the bottom rack, and unscrew the bottom spray arm. Inspect inside the spray arm housing to find the impeller, which is like a small fan. Clean away any objects or residue that might impede or clog the impeller or spray arm.
  
  

Obstruction

• Once all debris or residue has been cleaned from the bottom spray arm, make sure the arm can rotate freely. If the arm cannot move, the dishes may not get very clean. Improper loading of dishes can block the arm, as can items that fall or hang down through the racks. Spin the arm before starting the dishwasher to ensure it moves without problem.