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. 4 q$ V3 N( V* q2 W/ `9 \+ a2 K. p
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Solution: turn off water supply and take the humidifier apart and clean it will stop the leaking. ; S1 o/ T6 l" R/ a5 T7 K+ X & E2 i1 U# m2 t' L) G. q: h7 {/ D( q& h1 `$ R
Otherwise, find a professional or change a new set.