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. 3 A) q3 C# ^4 c0 p j ( m1 i2 N I$ n/ F* d3 P8 x/ bSolution: turn off water supply and take the humidifier apart and clean it will stop the leaking. ' Z, p" l Z: H5 d5 B( X, R + }: A6 X9 A" d0 W' r! ~ / _/ H1 s2 I! i9 W* b7 x5 JOtherwise, find a professional or change a new set.