Possible Causes:
The Dial on the Heat Sealer may not be turned up high enough. In order to seal the XT4 Bag, the dial must be set at approximately "6."
The heating element is broken. On the sides of the Teflon cover are two shiny metal strips that keep it in place. Loosen the screws that keep the two strips tight to the base of the heat sealer and remove the Teflon cover. Check to see if there is a break in the heating element. If there is, take the extra heating element from the box that the heat sealer came in and replace the defective element.
The insulator is not properly installed. The insulator should be installed to ensure that the heating element does not touch any of the metal on the base of the heat sealer.