F18 means the drainage pipe is blocked. Bottom right of the machine is a small door. Remove this, pull the stop out of the rubber pipe to drain out the excess fluid. There could be a lot so be prepared!
Next, unscrew the cap on the front feel inside for anything hanging about. I've gotten 5p pieces stuck in there several times. Once found, screw the cap back on, put the stop back in the pipe and replace the cover. All is well in Bosch land once again.