Methods and systems for performing an upper rack wash in a dishwasher

In one aspect, a dishwasher having an upper rack wash operation is described. In one example embodiment, the dishwasher comprises a tub, and a fluid circulation assembly for circulating water. The assembly comprises a pump, a lower spray arm, and at least one other spray arm. The at least one other spray arm comprises one of a mid level spray arm and an upper spray arm. The pump is in flow communication with the lower spray arm via a water passage, and the pump is in flow communication with the other spray arm via a conduit that permits water flow around the water passage. The dishwasher further comprises a water flow blocking mechanism comprising a water flow blocking device, a magnet positioned outside the water flow path, and a magnet positioning device coupled to the magnet. The water flow blocking device is normally positioned in a pocket in the conduit. The magnet positioning device is configured to cause the magnet to move from a first position to a second position. When the magnet is in the first position the water flow blocking device is maintained in the pocket by magnetic forces from the magnet. When the magnet is in the second position the water flow blocking device is not retained in the pocket by magnetic forces of the magnet.