If your windshield washer continues to spray continuously, there are two possible causes: either the valve is broken, or you've connected the hoses in the wrong direction, so that air pressure continually pushes the valve open.
If the washer stops spontaneously, or if you find a leak, you'll need to replace the valve, as repair is not possible in most cases. To do this, you can buy an entirely new switch, which is listed in the "related" tab, but if everything else still works fine and you're still happy with your current switch, it may be sufficient to replace just the valve.
Note: Carefully disassemble the valve and reuse the pressure pin if it's not included.
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