I had the same problem turned out to be the water inlet solonoid not shutting off the mains correctly. So when the machine was idle the water slowly entered and overflowed into a small catch tank underneath, activating the pump and bringing up the "OF" or overfill in the digital display. This is a safety function to prevent your kitchen being flooded. The book said service call, but being a "sparkie" how hard could this fault be? So after isolating the unit from mains power and water I swapped the two solonids around (behind the left hand side lower cover after sliding the dishwasher out from under the bench - inbuilt unit) and after a week no problems. The unit even functions okay as it is now, although I'm getting another solonoid valve and put it back as it was. As I am a licenced Electrician, before attempting any repairs ensure you are competant, if not get help. DO NOT put yourself at risk of injury trying to save money, the costs are too high should you fail to identify a hazard.
Davo the sparkie, May 2010