Try using fluid with a lower freezing point. The 3 for 2 ready mix from a well known shop is only down to -6 and what happens is it exits the jets, some residue fluid hangs about the jets and is hit by the cold air and freezes, preventing more fluid coming out. You can make up your own fluid using ammonia/water/white vinegar solution as Ammonia freezes at -79 so even diluting down to 1 part to 4 parts water will keep it at -20. When buying fliud from shops, look for the ones with 'highly flamable' warnings as they will contain higher concentrates of alcohol. Think Vodka in the freezer... it doesn't freeze in your freezer, so high alcohol content in washer fluid helps reduce freezing.