E28 means your Bosch’s Aqua Sensor (the turbidity/clean-water sensor) isn’t happy. That sensor watches how clear the water is and tells the control board to extend, shorten, or repeat rinses. When it can’t read correctly—because it’s dirty, starved of clean water, or failing—you’ll see E28 and usually notice things like cloudy glasses, long cycles, or extra rinses that never seem to finish.

What usually causes E28

Most of the time it’s not a dramatic failure—just a sensor that’s coated with film, a sump full of debris, or water that isn’t circulating cleanly. Less commonly, low water flow (partially closed valve, kinked hose, or a sticky inlet valve) will make the sensor “think” water is dirty. True sensor or wiring faults happen, but they’re rarer.

Quick checks

Unplug the dishwasher or switch off the breaker before touching anything inside.

• Water in: Make sure the supply valve is fully open. Straighten any kinks in the inlet hose and listen for a clean, quick fill when a cycle starts.
• Filters & sump: Lift out the filter set, rinse it thoroughly, and feel around the sump for seeds, foil, glass, or sludge. A dirty sump = dirty readings.
• Aqua Sensor: On many models it sits in or near the sump/tub wall. If you can see it, wipe the window gently with a soft cloth. Don’t scratch it.
• Reset: Power the machine off for a few minutes, then restart. If the fault was a one-off reading, the code may clear.

A more thorough, still DIY approach

Run a hot cycle with the machine empty and a dishwasher cleaner or a cup of white vinegar (top rack). This removes the biofilm that coats the sensor lens and tricks it into “seeing” dirty water. Next, check spray arms: pop them off, rinse them, and clear any blocked jets with a toothpick—poor spray equals poor rinsing, which feeds bad sensor data. If you have hard water, consider a descaling run; mineral film on the sensor is a classic E28 trigger.

If you suspect low fill, start a cycle and open the door 2–3 minutes in: there should be a healthy pool of water just under the door lip. Too low? Revisit the inlet valve, screen, and hose. Too high or sudsy? Use less detergent and make sure you’re using a dishwasher-safe product.

When the sensor itself is the problem

If E28 returns immediately after a proper clean and the dishwasher otherwise fills and sprays well, the Aqua Sensor may be failing. It’s typically a small turbidity module with a wiring plug. Replacement is straightforward for experienced DIYers but does involve removing panels and seals; if you’re not comfortable, this is a good hand-off to a pro. Also check the wiring harness for corrosion or loose pins before condemning the part.

Preventing E28 in the future

Rinse the filter weekly, clean the sump monthly, keep spray arms clear, and use the right dose of detergent and rinse aid. If you’re in a hard-water area, add regular descaling to your routine or use a softener—both help keep that sensor window crystal-clear.

One last note

Error codes can vary slightly by series and year. If your user manual lists E28 differently, follow the manual’s guidance—but the steps above still help because they restore clean water flow and a clear sensor, which is the root of most E28 complaints.