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The first thing to check is that the water/screen wash in the bottle is not frozen, in the weather conditions we are experiencing at the moment, even the best screen wash is freezing.
If it is frozen, you will need to thaw out the water in the bottle and in the pips before you can go any further with a diagnosis.
Once the washers have defrosted, try them again, they may work, if not check the fuses in the fuse box inside the van below the glove box, particularly fuse number 43 and 56.
If the fuses are ok, check that you have power to the pump, to do this access the bottom of the washer bottle by removing the wheel arch liner inside the arch, and remove the plug from the pump, using a multi meter or a power probe, connect one lead to each contact inside the plug (not the pump) and operate the washer switch, you should have 12-14 volts there, if you do, then the pump is faulty or possibly still frozen.
Defrosting the washers can be done by leaving the van in a garage with a heater on or just by leaving the engine running for a period and allowing the heat from the engine to defrost the water, dont be tempted to pour boiling hot water in to the bottle as this may crack the bottle, if the bottle is not full you can also add some neat winter screen wash, this will help to penetrate the ice and defrost it faster..
Hope this helps, if you need more information, please let me know.