Update. Appear to have fixed this issue. Knocking the pump worked for a bit. There was gunk in the tank from previous additives. I fixed by running compressed air down the line. Remove the joining top left under the bonnet to do this. I did it for about 5 minutes. Then I emptied the bottle and put d...

I had this problem. Pump can be heard running but no water coming through. The non return valve is a possibility but before you get one from Nissan at £26 try knocking the pump and give it a wiggle. There apparently is some sort of diverter that sends water to the front or rear and it gets stuck. Di...