Not using your Bosch dishwasher for extended periods (a few days or longer) can sometimes cause problems, and these often appear as some kind of drainage issue. Typical issues you might encounter when your dishwasher is left unused are the dishwasher basin slowly filling with water by itself, and/or the water draining when you try to start the dishwasher again, but the intake pump just runs continuously without water actually entering and the wash cycle never actually starts.
The are two likely culprits for these problems.
The first is the dishwasher drain hose, which may be allowing water to back-flow into the basin. Check the hose (usually under the sink) and ensure it has a high loop – as high as possible, but at least above the point where it connects to the sink plumbing. Examine the hose for any kinks or snags which are preventing the dishwasher water draining efficiently. The hose may also be clogged with debris or grease. You can try to clear this by agitating the hose to loosen blockages, or adding hot water to the dishwasher basin: when the water is pumped out through the hose it can breakdown or wash away any obstructions.
While the drain hose itself may not be blocked, there are plenty of other places that can get clogged up with grease, so check all connections and filters to make sure they are clean and allowing a clear flow of water. If you spot any problem areas, a good clean and hot water are the most effective way to get things flowing again.
The second is the drain float switch which can get stuck in place, especially if it hasn’t been used in a while. In this case the first thing to try is, as above, fill the dishwasher basin with hot water and run a cycle. As the water is drained it may agitate the switch back into action. If that doesn’t work you can try and reset the float switch manually. Refer to your dishwasher manual to find the exact location of the float, but as a starting point it will typically located at the bottom front of the dishwasher, behind the kick-plate.
If you don’t fancy opening up your dishwasher to find the float switch, you can also try ‘the tip trick’ – pull the dishwasher out from under the counter and tip it forwards by about 45 degrees. This will get rid of any remaining water that has settled at the bottom of the unit and doing so will reset the switch. Obviously this is not an option if you have an integrated unit. It also goes without saying that when you tip the dishwasher there is likely to be a lot of water coming out, so get ready with plenty of towels on the kitchen floor before attempting this!
Once your dishwasher is back up and running there are a few simple things you can do to help ensure the problem doesn’t reoccur. Firstly make sure you run the dishwasher on its hottest setting from time to time. The cooler eco cycles are great for saving energy, but the water won’t get hot enough to clear any grease and gunk that builds up. Make sure you check the filter regularly and don’t leave any debris you spot in the basin. This could eventually find its way down below the filter and cause a blockage which will lead to drainage issues reoccuring. Finally try to run the dishwasher regularly. Allowing it to sit unused for long periods increases the chance of the drain float switch becoming stuck in position.