Hi. I fixed my Nautilus when it had this same problem. Was a bit tricky getting off the inner front panel (you will have to remove two) but all up took about 30 - 40 minutes. Found that the flood was caused by accumulated gunge where the hose was attached to the sink pipe. When you get off the second panel unclip the earth lead and remove the foam insert (if there is one). There are multiple coloured electrical leads to the various parts of the motor etc. The leads to the flood switch are black and yellow. Follow them back and you will find the flood switch itself. Just jiggling it around was enough to reset it. hope this helps.
Jane
October 2008