JBJ Auto Top Off keeps pumping water

[Nasoblond]

So...was very lucky last night that I just happened to notice that my auto top off would not stop pumping water into my sump. I was pretty quick to unplug it to avoid a huge mess in my living room. It seemed really odd that it would do this as it has never failed for about three years that I have had it. Do these just go and need replacing?
I took out all the sections and cleaned them and put them back in tonight and the same thing happened all over again when I plugged it in. Is there a repair trick I am missing or do I just need to buy a new one? I don't think its the float things that go into the water.....it may just be the controller that's shot?
Any suggestions?
Thanks