Tried the heavy weight, seems to work for about two days then starts
pushing up.

I agree the central heating will shrink the planks, i was amazed how
much they did shrink around the edges of the wall under the skirting
boards last winter. (did a proper job removed the skirting boards,
that wasnt easy but better looking).
I am tempted to remove the skirting to see if there is a gap around
the edges i know i had left some expansion, maybe not enough.