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. ( V6 w$ \- m1 P, R" y! H) v& ^; B4 O$ R' L e9 v# O& G4 O
Solution: turn off water supply and take the humidifier apart and clean it will stop the leaking. $ u0 I0 o2 M8 ~, i/ Z$ X 4 P! S3 X4 M: A4 z2 ?6 q4 d. c, ^/ a7 N
Otherwise, find a professional or change a new set.