Any station that you want to activate the master valve needs to be flagged to do so.
To change the setting of each station, tap the gear icon next to the station name. If you are using the recently updated UI with the new home screen this can be done right on the home screen. Otherwise, you will find this in the “edit stations” page.
Oh, I neglected to ask which firmware you are using.
The Pi just recently started supporting the Arduino firmware now known as unified firmware. This is the firmware I write the UI for which is also used on the mobile applications. This is the firmware that recently got an updated UI.
Both firmware’s have some sort of auto update at this point. The unified firmware can auto-update the UI/front-end while Dan’s Python firmware can do entire firmware updates from the UI or automatically (using plugins).