When I close the DUO carbonating head, there is a small gap and it seems like it is not properly closed; what should I do?

As part of the safe design of the DUO Sparkling Water Maker, a small gap (about 2 mm) remains when closed. This just means the flask-locking mechanism is working properly and allows for easy movement between the flask ring and the flask. If you still feel the carbonating head is not closed properly, reopen and close it again by holding the top of the carbonating head down while locking the flask.