Hi Rob,
Have you ensued that you have pushed the upper silicon in the top float firmly in the recess and made sure that it is creating a parallel seal on the hole below, this will ensure that it floods and drains correctly.Hold it at eye level to see that it is sitting on the hole below correctly. Also ensure the tray is empty before you carry out this procedure …. always place an AQUAvalve in the tray when no water is present. Regards Josh