Nexus Automatic does not close waste valve

To locate the issue you will need to:

Check the relay furthest on the right in the auto box -
Check the fuse - Does it light up during a cleaning cycle?

If the relay is working as it should, you will need to check the motor. If it’s under warranty you will need to report back to where it was purchased from with a copy of your receipt and they can organise a replacement. However if it is out of warranty you will needs to purchase a new motor.