@dario I had the same issue, using UiFlow Beta as a version I see UiFlow 1.8.2 and for both Core2 as well as Fire I can see and add them (the THERMAL unit).
Only issue I personally now have is that I have a pretty unstable connection from the Fire or Core2 to the web IDE so I can't really apply the 1.8.2 blockly code. And the Desktop IDE at the moment is stuck at 1.7.5 that can't handle the files I save using version 1.8.2.
Maybe for you with a stable UiFlow internet connection you can use version 1.8.2 to test and deploy your Thermal code.
Make sure to ofcourse burn 1.8.2 to your device also.