It is possible that the shut-off valve was blocked by the cumulated white stuff. As a result, water supply can not be stopped even when water level is high. . k; J& s. l+ w' b( V f
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Solution: turn off water supply and take the humidifier apart and clean it will stop the leaking. 9 z k k Z$ \* ~+ @) G) u, M, U5 ~; W k4 c# P! j& ~
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Otherwise, find a professional or change a new set.