Rule Mate 500 Auto

[Safari38LH]

I have just installed a Rule Mate 500 Auto pump in my bilge on a Little Harbor 38. The bilge is not that large and the pump might be 4-5 or so feet below the outlet which is above water. I first installed it without any check valves but the pump when on auto will not turn off after pumping everything out. If I switch it to manuel and then back to auto it does stay off. I thought maybe the "head" of water still in the hose was causing this so I did install a check valve. Unfortunately the pump still will not shut off on it's own. I did try the pump in a bucket and it does turn off correctly after 5-10 seconds when taken out of the water so then float does work in perfect conditions.

Any ideas? This is the new Rule Mate 500 with the special no oil float.