New Wash is different from detergent shampoos and so it requires a little shift in how you wash your hair.
If your hair is feeling greasy or you've got some build up there are two common reasons:
You might not be using enough product. Apply New Wash to coat or cover hair like you would for a conditioner or mask. Then work it in really, really well. This will allow it to capture and bond to the dirt, build up and excess oil.
You might not be rinsing it out thoroughly. New Wash bonds to the bad stuff and requires quite a bit of rinsing to work it out. Massage it out with finger tips or the brush.
New healthy habits and routines take time to get into a groove. You might have a transition period during which your scalp is over-producing oil (like it was trained to do when you used detergent shampoo) because it hasn't acclimated to this new way of cleansing that leaves the healthy protective oils to do their job.
After about 2-3 washes (max 10) you're scalp and oil production will regulate and thrive with your new healthy habit!