Navien, ESP32 Navilink interface

Connector 1 (RSS – main communication/power connector):

1.GND
2.Not connected (NC)
3.A (RS-485 Data +)
4.B (RS-485 Data -)
5.~14V (heater-provided power – not used in my setup; powering externally instead)

Connector 2 (auxiliary):

1–4. (unused in my config)
5. 5V

Yes, you’re spot on with that observation!

I’ll upload clearer pictures of the connectors once I get a proper mating connector (currently using temporary wiring).
Also, my previous YAML code is still missing the direction pin to properly control the TTL-to-RS485 transceiver (DE/RE for transmit/receive switching). That’s the main thing holding back full bidirectional communication right now.