As others have said, a slight gap between the lid and kiln body is normal. You will see light under the lid due to that gap. However, something is wrong if the lid rises in the front.
A gap forms under the lid because the center of the lid bows inward slightly as it gets hot. This happens because the outer surface of the lid is cooler than the inner surface, so the lid expands more on the hot inner surface.
If the lid actually rises in the front, the hinge may be bent. The hinge should have play in it to allow it to remain flat against the kiln. Without the play, the lid can rise 1/4" or more at the front.
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Arnold, There is more then a 1/4" gap up to 1/2". I will check the hinge, I am suspecting that may be the problem. I am not sure if it is an adjustable type of hinge or not. Does a draft play a part in the lid staying flat? I have my kiln in my garage with just natural airflow (garage door open a foot and the back door open about a foot also). I am so very grateful for finding this community~ what a great support for budding artists.