we had a couple of issues with our bosch dishwasher
1. clogged grain led to the dishwasher overfilling and leaking
2. after unclogging the drain, the dishwasher would not operate or fill with water. additionally, the drain pump would continue to operate at all times even with the door open.
3. we had a "4" error code - water level

after reading up on this and other forums, i thought i had narrowed down the problem to a water inlet valve or the water level float switch

it turns out the problem was quite simple.
bosch incorporates a plastic pan beneath the dishwasher to capture water spills, thereby saving your kitchen floor (in theory)
well there is a float switch arm in the pan that activates the water level float switch, preventing the water inlet valve from opening if there is water present in the pan (there was). this would prevent the dishwasher from continuing to overfill the dishwasher and perpetuate water spillage underneath the washer. pretty ingenious really.
sop up the water in the pan with paper towels or dish towels and viola - return to normal function as if nothing ever happened.