Yeah, this was my thought (the fact that it’s just a relay), and I figured I could connect it’s output to the load to the switch pin on a relay instead. I am gonna look into this possibility, since it would allow for some sort of local control if things go down. My thought is I could set the temp on the physical therm to way below the target temp (in the heating months, above the target temp in the cooling). This way it kinda also acts as a fail safe. And if HA is down and we need to override it, we can. Might need to put more thought into this though.

Also, here is a Z-Wave relay I use for another project and it works well, just FYI Zooz ZEN51

Yeah, this is something I’m also toying with. Just get a relay and temp sensor and fake it out.

However this is not my first choice, as I prefer to still have control of things if HA is down or something. So I wonder if I could wire it in with the existing therm to provide the ability to override. Like when adding a real to a switch.

I don’t have control of the water temp, but I have pseudo control of the heating cooling by just turning it on or off. Which is pretty much the same premise as “normal” HVAC.