Hi, my name is ***** ***** I can help you with this issue. Knowing how to use the flue correctly is very important to maintaining your fire and your enjoyment of the warmth it provides. Here are several ideas for you to try:
Can you see the flue open and close when you look up inside the firebox at the top? Usually as you move the lever up and down you can see or hear whether it's open or closed. You can hear a suction sound on a breezy day, like it's drawing air up, and that means the flue is open.
To determine if the flue is open or closed, have you tried holding a lit lighter near the top of the firebox, and then moving the lever up and then down and watching what the flame does in each case? If the flame acts like it is dancing, the flue is open.
Have you read the manual that came with the fireplace? It should tell you which way is open or closed. If all else fails you can call the fireplace's customer service phone number and they will be able to tell you.
I found this too, and on page 13 it tells you how to open and close the flue, except here it is a dial rather than a lever: http://www.manualsdir.com/manuals/123192/majestic-appliances-nvbc36-nvbr42-nvbr36-nvbc42.html
Does this answer your question? If not, we can try something else. Thanks,