@adamfilip said in Tool vs Bed Heater activation:
But Tool 0 is already selected, by default
Does it have a little underline underneath the word "Tool 0"? If it doesn't it's not active so you need to click on it to make it active. It's a bit confusing because the next column in "Heater" and that may well say "Active". I have 5 or 6 tools with my mixing hot end so I've learned to look very closely at the "Tool n" to see which one is active. I know the Chris Ham has it on his list to make the active tool more obvious.
It behaves differently to the bed because most printers only have one bed, but many have multiple tools.