Pull it out and set in on your counter. Plug it in and see if it works. If it does, then I would suspect a problem with the installation, not enough airflow. If it's still not heating, you have to pull the cover. I hesitate advising pulling the cover on a microwave because there is lethal high voltage in there. Even when unplugged the HV capacitor can hold a deadly charge. If you still want to pull the cover, let me know and I'll tell you what to do.