The valve is as far clockwise as I can get it, I will take it off tomorrow and see if it is faulty. Thanks for your help!
They aren't expensive so you can get a replacement from any pumping supply store.
Purefreedom drill a tiny 1mm hole through the paddle to stop you closing the valve completely and damaging the r/o membrane. So never completely shut the valve off if you replace it.
I took the valve off today, and although it opens and closes properly, the 1mm hole is more like a 5mm hole! So I think this must be the problem. I couldn't get a replacement valve from my local plumbing store as it is 1/2 inch and they only stock 15mm. So I got a hozelock sprayer and attached it to the end of the waste hose and turned it to a fine mist spray which slowed the waste production right down, and has increased my pure production up to about a litre a minute without the use of the pump, which I am very pleased with! So thanks for the help guys!!