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. 9 o& W: f) ^! B0 R0 }% t( d+ }- s: V% L% Y7 M" P
Solution: turn off water supply and take the humidifier apart and clean it will stop the leaking./ @3 t! ]! R. Q8 D
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Otherwise, find a professional or change a new set.