Check the Solenoid Valve.
Open the front cover of the Backup in a Box Control Unit.
Is there a humming noise coming from the soleniod valve which is located on the right hand side of the unit and has the mains water supply plumbed into it.
If yes then there is a fault with the solenoid valve and you will require technical assistance.
Please turn the power off to the Backup in a Box and contact us.