Can it be held closed tightly? I mean, is it a case of not pulling shut or the door has warped or something.
I would guess there is some sort of spring mechanism attached to the door hinge that pulls it shut properly. That spring has probably lost some of its "springiness" over time due to being repeatedly heated. You may be able to open it up, find the spring and refashion it, or just shorten it a but. It really depends on how much effort you can put into it, and the actual shape and style of the spring.