I had the same problem (the empty water light flashing continuously) - after dismantling the pump housing (bottom right at rear) I found that some polystyrene balls (from the float? - great design there!) had come loose and were stopping the float dropping back down (the float rises and trips a micro-switch when the reservoir is full).
since they've all been removed, I haven't a repeat of the problem.
Pat Richards, January 2007