how can I fix my Dishdrawer model DD603H?

My Dishdrawer comes up with fault F1 when it is in standby and not being used. There is no water leak onto the base so the flood switch is dry. Could it be a faulty flood switch? I have just purchased this machine second hand and was told that it did have an F1 fault but it ran fine for 3 washes on each drawer when I installed it and had been standing idle for nearly 24 hours when it just suddenly alarmed and started flashing F1.