I had a problem with no screen wash water (Micra K11) although I could hear the pump operating. It also made two slightly different noises, when supplying front screen and rear screen. I found that there are at least three "non return" valves in line - on mine, one is on the bonnet lid, before it splits to feed the two front jets. Just remove it and clean it out (or replace it..). I found one behind the o/s front inner wing liner, which did the same for the rear line, and then another one in the tailgate. To get the tailgate one, i had to disconnect the hose at two points - the flexi connector on the left top inside of the tailgate, and by the squirter, then use a bit of string so that I could remove the hose between them (and replace it afterwards. I found the non-return valve partway between the two ends. Cleaned and de-gunged, replaced, and everything worked again. Hope this helps!