I had same problem, but after fiddling with the top for a while, after it had gone cold, some slight movement occurred, and I was able to gently unscrew - I've also greased the thread - I think there seems to be a grub screw which might need tightening. good luck
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I had same problem, but after fiddling with the top for a while, after it had gone cold, some slight movement occurred, and I was able to gently unscrew - I've also greased the thread - I think there seems to be a grub screw which might need tightening. good luck