In short, the combustor needs light-off temperature before the by-pass should ever be closed.
A temperature of 500 degrees F. must be focused on the catalytic combustor for as least 25-30 minutes before the by-pass is closed. This will assure you that the combustor has had ample time to light-off. This is just a rule of thumb for any catalytic stove. Remember to read the manufacturer's manual before building the first fire in you stove or contact Applied Ceramics.