(just re-posting from the other thread - so ignore if you’ve already read!)

It’s a TRV head. You can unscrew it with the ring under the black area - may need an adjustable spanner to loosen. When you take it off, see if the rotation works and that the pin inside moves up and down. You can also check the metal pin/valve where it attaches isn’t stuck (it may need quite a bit of force to check - could need whacking with a hammer if it’s actually stuck). If everything seems OK, re-attach the head and see if it’s working. If it isn’t, new heads are cheap. What you have looks like what I have - cheap generic TRV heads, easy to find online.

Yeah, same. I set it up as it looked like the best way to control my inverter - I wanted to set it to charge from the grid when electricity was free, and discharge during saving sessions without having to do it manually. I then expanded to trying to calculate how much charge I needed overnight in cheap rate based on the solar forecast for the next day…

Anyway, I now have everything on it and keep thinking of things to add.

I didn’t know anything about this, but I found some English documentation here which explains it: http://www.atarimania.com/utility-atari-st-gemini_35572.html