Stiebel Eltron uses CAN Bus for their communication with external devices like FEK remote control or ISG gateway. And CAN Bus is a standard that can be used with ESP32 too using an MCP 2515 can bus controller.
If you have a look at the heat pump’s manual in the section for electrical connections - for me it is section 12.2.3 and 12.8 you can read, how an ISG should be connected to the heat pump.
In the same way as the ISG, you can connect an MCP2515 CAN Bus component via an ESP32 microcontroller as set up in my thread. ESP32 is easily integrated in home assistant using ESP-Home.
To receive the corresponding signals from the heat pump, you send a hex command over the CAN Bus interface and the heat pump answers respectively. The needed command keys are located in the file “ElsterTable.inc” on the website juerg5524.ch.
Such a send command can look like this in ESP-Home.
- canbus.send:
data: [ 0x31, 0x00, 0xfa,0x09,0x22,0x00,0x00 ]
can_id: 0x680
The first and fourth digits are used to signal the request to the address of the heat pump - here it is the address ,3*8 + 0 =18 + 0 => 180.
Sencond digit “1” means request.
Digits 5 and 6 are usually “fa” with some certain exceptions, when the Elster Index is smaller than ff ff.
Digits 7 to 10 “09 22” is the Elster index key listed in the ElsterTable as “WAERMEERTRAG_2WE_WW_TAG_WH”.
As an answer you’ll get something like d2 00 fa 09 22 xx xx, meaning answer (digit 2 = 2) to can-id 680 (d*8 + 0) for request 09 22 and xx xx the value of the heat pump in double.
For any further questions, please follow up in my thread, as I think it is better discussed there.