I never heat my molds. I always suck my plastic up from the cup i do heat my injector good and warm. Pull slow to fill injector u can pull air in when u force it. If u are not getting any flash when u tighten lite hand tight that maybe the way to go. U might want to run a pick down the vents. Did u change brands of plastic. Or switch to a different gallon. Might mist your mold with a little worm oil. Just drawing straws.LOL Cub48