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oddbean The limescale does look like it’s on the upper nut. The bigger concern is what appears to be a crack in one of the elements. I had a knackered element on a machine I bought and it was cracked like this. The switch looks like it has been changed, combined with the element, I suspect someone let it run dry which usually breaks the element and can also short the switch. One of the elements could still work but the machine won’t heat up properly with one element so you will need to change it.
The machine looks nice but £300 seems a lot if you’ll end up spending another £100+ to get it working
The wiring also looks brand new.