I had same trouble and blowing through with compressed air was only a temporary fix. Using a tiny drill (<1mm) to remove the blockage out of the nozzle worked well.
Cheers, Farmbenz
I'm not brave enough to dismantle the nozzles as its a job and a half to put it back. What you you can try is add a few DROPS of household bleach to a nearly empty washer tank. Obviously you'll have to try discharging the tank by undoing the washer reservoir pump. After you've added the bleach, leave overnight and then fill up with cold water (dont add screenwash). Then, activate your washer in a continuos stream and it should flush through.
A 1mm drill bit is not a good idea as the jets are only .78mm.
Instead, you should try some electrical fuse wire (still sold in DIY shops) to reach deep into the jets - needles are just 2 or 3 inches long.You need to reach further to dislodge any sludge build up. You may have to repeat it several times
Give it a try but dont forget to wash off any wash mix that comes out from your nozzles. Good luck