Super-Huge thanks to everyone that replied in this thread - the job is done and the line has been capped! I'm glad I asked which direction the nut should move in because the answer I got was the opposite of my intuition, but I turned it in the suggested direction and the fitting quickly became...
Like I said I don't want to do any soldering in my furnace/water heater closet. I'm probably just being paranoid about that but it seems I can solve this problem without soldering.
I really like the idea of just leaving the compression nut and ferrule in place and just replacing the current...
First off I should say that this will be my first ever plumbing project of any kind whatsoever, so any help is greatly appreciated.
I recently bought a house and even though there were no appliances, there was a flexible copper line coming directly out of the main that was tagged "ice maker"...