How to unfreeze frozen bunk cushion zippers??

[Cruiser1]

I have just started to look at replacing the foam in a few of my bunk cushions. The covers are still in good condition so I just want to unzip them, get the new foam cut to size to match and slide it in. Trouble is some of the zippers are frozen up - as on most boats i guess

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Has anyone used heat or some other technique for kicking the zippers back into action?

 

[Justin_NSA]

Good luck. i ended up having to get one zipper replaced. it was still worth it to have fresh padding