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. $ p$ ] E6 @" L( f$ h) n7 Y/ @1 s0 U( M G9 c
Solution: turn off water supply and take the humidifier apart and clean it will stop the leaking." O3 w3 }1 G H; w; `( Q
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Otherwise, find a professional or change a new set.