If you've been going fast and furious, it may be too hot. Some units require a short waiting period between each sealing. Don't know the specs on yours, so this may not apply. Check the manual to see if your unit requires a pause.
This thought is in addition to Wayne's. Juices or powder (if you sealing dry stuff) may have something clogged.
Just 2-cents. Hope you get it working soon.
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