I’m wondering if anyone has reverse engineered Takagi’s TK-x remote control protocol. Takagi uses a twisted pair for remote communication with any of the TK series tankless water heaters out to a TM-RE30 remote controller. The TM-RE30 is able to report inlet and outlet water temperature, flow rate, set point, time, and error codes. Up to this point I have only checked for the presence of DC (measured at about 15VCD) and the presence of an AC signal in the mV range. I have yet to put a oscilloscope on the line to determine the frequency of the AC or to capture any signaling. My interest is in integrating this information into a centralized residential energy management system.