verified connector library

Stiebel Eltron WPM3 heat pumps (needs ISG web gateway, Modbus TCP)

Register map(s) for this device, each at the trust rung it earned. Addresses are 0-based as on the wire. Word order and scaling are confirmed at the hardware-verified rung and at no rung below it.

interop-verified

Read + decoded cleanly over a real network vs an independent third-party Modbus test server (transport and framing; reads are remapped into the server's register window, so the map's own addresses are NOT exercised). Does NOT prove word order/scaling against the actual device.

pointaddress (0-based)typescaleunit
actual_temperature_fe7500I160.1°C
set_temperature_fe7501I160.1°C
outside_temperature506I160.1°C
actual_temperature_hk_1507I160.1°C
set_temperature_hk_1508I160.1°C
actual_temperature_hk_2510I160.1°C
set_temperature_hk_2511I160.1°C
actual_flow_temperature_wp512I160.1°C
actual_flow_temperature514I160.1°C
actual_return_temperature515I160.1°C
actual_buffer_temperature517I160.1°C
heating_pressure519I160.01bar
flow_rate520I160.1l/min
actual_temperature_dhw521I160.1°C
set_temperature_dhw522I160.1°C
source_temperature535I160.1°C
source_pressure537I160.01bar
hot_gas_temperature538I160.1°C
high_pressure539I160.1bar
low_pressure540I160.1bar
operating_mode1500U161
comfort_temperature_hk11501I160.1°C
eco_temperature_hk11502I160.1°C
comfort_temperature_dhw1509I160.1°C
eco_temperature_dhw1510I160.1°C

link settings as documented (unverified): TCP; unit ID 1; FC 03,04,06,16; ISG standard IP address: 192.168.0.126, TCP port: 502, Slave ID: 1 (permanent). ISG addresses are 1-based.

⚠ Incorrect use can result in damage to the connected integral ventilation unit or heat pump. For safety reasons, faults can only be acknowledged via the SERVICEWELT user interface. — Starkest reads only; we never write a control register.

bench facts as documented (unverified)
connectorRJ45
wiring notesIP network connection to the ISG and to the building management system
broadcastnot supported
sentinel values32768 (0x8000H) for unavailable objects
protocol notesFor appliances of the LWZ series, the WPM displays substitute values '-60' (sensor lead missing/disconnected) and '-50' (short circuit of sensor lead).
identification notesChecking the software version: SERVICEWELT under DIAGNOSIS -> SYSTEM -> ISG
firmware applicabilityWPM 3 with software version 39005 or higher, and WPM3i with software version 39106 or higher.

⚠ disputed: set_temperature_hk_1 @ 508 — disputed by Stiebel Eltron Modbus TCP/IP Software Documentation. For WPM 3 and WPM 3i, SET TEMPERATURE HK 1 is at address 510 (1-based), which is 509 (0-based). Address 509 (1-based, 508 0-based) is only for WPMsystem [3.1.2].

⚠ disputed: hot_gas_temperature @ 538, high_pressure @ 539, low_pressure @ 540 — disputed by Stiebel Eltron Modbus TCP/IP Software Documentation. Addresses 539, 540, and 541 (1-based) are only supported on WPMsystem. For WPM 3 and WPM 3i, these parameters for Heat Pump 1 are located at 544 (1-based / 543 0-based) for hot gas temperature, 545 (1-based / 544 0-based) for low pressure, and 547 (1-based / 546 0-based) for high pressure.

field reports — community-sourced, unverified (checked 2026-06-11)
  • The official Stiebel Eltron documentation uses 1-based register addresses, which causes off-by-one errors (offset of 1) when integrating with 0-based Modbus clients. [source]
  • The Modbus TCP/IP software interface cannot be combined with other ISG software interfaces (e.g., ServiceWelt remote monitoring), except for read-only access alongside the EMI energy management extension on firmware v12.1.2 or higher. [source]
  • Home Assistant integration setup fails with a fatal error ('ModbusClientMixin.read_input_registers() got an unexpected keyword argument slave') following updates to pymodbus v3.10+ due to the removal of the 'slave' parameter. [source]
  • confirmed: ISG standard IP address: 192.168.0.126, TCP port: 502, Slave ID: 1 (permanent) — confirmed by Stiebel Eltron Modbus TCP/IP Software Documentation [1.3.4] and TapHome integration guide
  • confirmed: ISG addresses are 1-based — confirmed by Stiebel Eltron Modbus TCP/IP Software Documentation
  • confirmed: WPM 3 with software version 39005 or higher, and WPM3i with software version 39106 or higher — confirmed by Stiebel Eltron Modbus TCP/IP Software Documentation
  • confirmed: Checking the software version: SERVICEWELT under DIAGNOSIS -> SYSTEM -> ISG — confirmed by Stiebel Eltron Modbus TCP/IP Software Documentation
  • confirmed: Substitute value '32768 (0x8000H)' for unavailable objects — confirmed by Stiebel Eltron Modbus TCP/IP Software Documentation
  • confirmed: For appliances of the LWZ series, the WPM displays substitute values '-60' and '-50' — confirmed by python-stiebel-eltron library source code
  • confirmed: Control warning regarding damage and SERVICEWELT fault acknowledgment — confirmed by Stiebel Eltron Modbus TCP/IP Software Documentation

The trust ladder

Each rung states what it proved and what it did not. Gray until proven; green is earned by hardware only.

If your device isn't here, upload its register map. Generation is free, and the connector keeps the rung it earns under testing.

To prove a connector against your own device, order hardware verification. If it doesn't verify, you don't pay.

Platform builders can license the verified library: machine-readable maps, the firmware matrix, API access.