To do dish washing we opted for a Bosch SMU68M05AU. We installed it ourselves in the kitchenette.
It worked well then one day we started to have this error code E:21 on the display and the Check Water light was on ;-(
What we also found was that at the end of each clean there were water remaining in the sump.
According to the manual I had to check the pump to see if something was preventing it from spinning. The guide also suggested that the hose from the dishwasher may be clogged which I found surprising as we only had this appliance for a few months.
Inspecting the pump I could not find any food or things that could have blocked it. I also detached the hose from the pipe under the sink to double check but everything looked fine there too.
Interestingly I noticed though that every time after I took the stagnant water out of the sump with a sponge the dishwasher would operate and clean my dishes. However at the end of the cycle there was still a few centimeter of stagnant water in the sump.
I was about to call Bosch customer service in but I thought I would reinstall the draining hose first.
Initially I had the hose coming from the dishwasher, through the bottom of the cupboard, attached under a shelf. I thought it might be the cause of the issue so what I did was I drilled a hole in the shelf and run the hose through it and re-attach it to the pipe under the sink. The result is that the top of the curve is like 20cm higher than before.
After this simple move our dishwasher has been working like it should for several weeks now. There is no stagnant water left in the sump at the end of the cycle.
Who would have thought that the hose needs to be installed higher?
If you have this problem try reinstalling the hose for draining higher up to see if it goes away before calling in customer service.