I have found the comments here interesting, as I know little of the technical details of the device. I know that it works and have discovered some problems with it through direct experience.
There ARE sockets on the top of the hex nut. The factory uses them to adjust the settings of the device. I don’t know how to adjust them, and I wouldn’t want anyone else to try.
I do know it can be reset to serve a light commercial water heater because that was its original intended use. Hope that helps.