Torbeck Ecofil filling valve

I have just fitted a new Torbeck Ecofil bottom entry valve. Have set it up as per instructions and done up the column nut, the water comes in and the float valve shuts, but after an hour the water level has crept up 30mm to the overflow.
Have tried adjusting the float and the water level but it still creeps up to the overflow pipe. Is the unit faulty, have emailed Opella for help but no response!
Can anybody know the anwser

The rubber 'o' ring under the "column nut" will be letting by, take it back or try some silicone grease