I'm sure I saw reference to this somewhere but for the life of me I can't find it ...

Is it possible to 'lock' an HR92 so that the temperature can't be changed by turning the dial ? I'd like to do this in the kids room so we don't go from freezing cold to 'summer in Sahara' by 'accident'
According to the instructions there's an icon for 'operation lock' but no description of how to activate it or what it does.