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. . q$ I5 g4 h/ ?2 J3 b1 h {! {- v# }6 K
Solution: turn off water supply and take the humidifier apart and clean it will stop the leaking. 6 {1 D" X: S& F) r- C; m9 h, x+ W; Y% s" Q- I; s) R' ^# n
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Otherwise, find a professional or change a new set.