Why are dishes on the top rack dirty while the bottom rack is clean?

Start with the top rack’s load and visible clearance rather than assuming the dishwasher has an internal fault. Items packed close together or a tall item in the wrong position may interfere with cleaning. Bosch advises leaving space between items, checking that tall items do not block spray arms, and following the owner’s manual for filter and spray-arm cleaning and upper-rack adjustment instructions [S1].

These are practical checks, not a diagnosis. They do not prove that a loading issue is the cause or determine whether an internal component is working.

Look at how dishes and utensils are arranged. Check whether top-rack items are crowded or touching, and whether a tall item extends into a spray arm’s visible path. If the manual describes how to check the arm, follow those instructions rather than forcing it or removing parts without model-specific directions.

For example, note whether the same type of dish is clean on the lower rack but dirty on the upper one. That observation can help describe the pattern, but it does not identify the cause.

Check whether your model has an adjustable upper rack and whether its current setting suits the load. Bosch recommends using the owner’s manual for the model’s upper-rack adjustment instructions [S1]. Don’t assume every model adjusts the same way or try a mechanism based on another dishwasher’s instructions.

For example, if a large plate or pan below appears to reach into the upper rack’s space, note that arrangement and check the manual before changing the setting. This is a fit-and-loading check, not proof that rack height is the reason dishes remain dirty.

You can include them in a maintenance check, but follow your model’s manual. Bosch advises cleaning the filter and spray arms according to the owner’s manual [S1]. The source does not establish how every model’s parts are removed or cleaned, so don’t improvise or dismantle anything.

To make the check useful, change one visible factor at a time. First leave more space between top-rack items, then note what remains dirty after the next load. If the problem continues, record the result rather than concluding that a particular part has failed.

Use this checklist, following your model’s manual wherever it applies:

1. Leave space between top-rack items.
2. Look for tall items visibly blocking a spray arm.
3. Check the manual for any upper-rack adjustment instructions.
4. Clean the filter and spray arms only as the manual directs.
5. Record which items remain dirty and where they were placed.

Copyable note: “Top rack: [which items were dirty]. Bottom rack: [clean or not]. Load arrangement: [brief description]. Visible spray-arm obstruction: [yes/no/not sure]. Rack setting: [setting or not adjustable]. Manual-directed filter or spray-arm cleaning checked: [yes/no]. Result after changing the load: [what happened].”

These observations can describe the pattern, but they do not establish an internal cause.