MBMap Registry
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  3. ISG web / ISG plus

Stiebel Eltron ISG web / ISG plus Modbus register map

Internet Service Gateway ISG web and ISG plus with the Modbus TCP/IP software extension: heat pump manager WPM 3 and WPM 3i system values, parameters, status and energy data

  • Official
  • 118 registers
  • Modbus TCP
  • Revision 1 · 2026-11-10

Official: Written from the manufacturer's documentation, but not tested on a device yet. Check the map against the manufacturer's documentation before you write to a live device. Tested it? Report a test.

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Communication

Protocol
Modbus TCP
Unit ID
1
TCP port
502
Byte / word order
ABCD · bytes big-endian, words high first
Addresses
1-based · wire address = address − 1

Connection values are defaults: the device may be configured differently.

Map

Registers
21 holding registers, 97 input registers
Groups
5
Translation tables
6
Revision
1 · 2026-11-10
Added
()
File
maps/stiebel-eltron/isg.mbmap.json · 29 KB · history
SHA-256
b560147f50b275d0be84aa04df812d52778e703c4c6406aae6a4a50ae379a1ca
Manufacturer
stiebel-eltron.com

Sources and notes

Source: Stiebel Eltron, Software documentation Modbus TCP/IP (Software extension for Internet Service Gateway), WPM 3 / WPM 3i chapter and chapter 10

  • Addresses are the numbers of the manufacturer's tables (for example 501 for 30501). The document says the ISG is one-based and that an offset of 1 may be needed depending on the client, so address_base is 1: the address on the wire is the number minus 1. If a read returns the neighbouring value, try address_base 0.
  • The register tables differ per controller: the manufacturer publishes separate tables for WPMsystem, WPM 3 / WPM 3i, LWZ (05.1, 07.1) Plus (ISG Connect only), integral ventilation units and WPM G (WPE-I). This map follows only the WPM 3 / WPM 3i tables plus the SG Ready registers; the numbers in other tables can mean something else.
  • Not every object exists on every device. An object that is not available reads 32768 (0x8000), shown here as a sentinel.
  • Temperatures and most setpoints are integers with a 0.1 scale; the values with data type 7 (pressures, heating curve slope, volume flow) use 0.01. Energy totals are split: total energy = MWh register × 1000 + kWh register (0-999).
  • The per-heat-pump values (addresses 542-583, 3523 onward), the cooling-circuit setpoints of WPMsystem, the fixed-value mode (1508), the reset registers (1520, 1521) and the power-limitation registers (4250 onward) are not in this map.
  • Default connection: IP 192.168.0.126 when connected directly, TCP port 502, slave ID 1 (cannot be changed). Modbus TCP/IP needs the Basic service package and cannot be combined with other ISG software interfaces, apart from read access next to the EMI extension.
  • Written from the manufacturer's document; not tested on a device.
AreaAddressNameTypeAccessUnitScaleDescription
IR 501 int16 R °C ×0.1
IR 502 int16 R °C ×0.1
IR 503 int16 R °C ×0.1
IR 504 int16 R °C ×0.1
IR 505 int16 R % ×0.1
IR 506 int16 R °C ×0.1
IR 507 int16 R °C ×0.1
IR 508 int16 R °C ×0.1
IR 509 int16 R °C ×0.1 Only WPM 3i; WPM 3 uses address 510
IR 510 int16 R °C ×0.1 Only WPM 3; WPM 3i uses address 509
IR 511 int16 R °C ×0.1
IR 512 int16 R °C ×0.1
IR 513 int16 R °C ×0.1 Only with a flow/return module (MFG)
IR 514 int16 R °C ×0.1 Only with a flow/return module (MFG)
IR 516 int16 R °C ×0.1
IR 517 int16 R °C ×0.1
IR 518 int16 R °C ×0.1
IR 519 int16 R °C ×0.1
IR 520 int16 R bar ×0.01 Only with a flow/return module (MFG)
IR 521 int16 R l/min ×0.01 Only with a flow/return module (MFG). The older document revisions list this with one decimal (scale 0.1); the current one lists two decimals
IR 522 int16 R °C ×0.1
IR 523 int16 R °C ×0.1
IR 524 int16 R °C ×0.1 Cooling
IR 525 int16 R °C ×0.1 Cooling
IR 526 int16 R °C ×0.1 Cooling
IR 527 int16 R °C ×0.1 Cooling
IR 528 int16 R °C ×0.1 WPM 3 only
IR 529 int16 R °C ×0.1 WPM 3 only
IR 530 uint16 R h WPM 3 only
IR 531 int16 R °C ×0.1 WPM 3 only
IR 532 int16 R K ×0.1 WPM 3 only
IR 533 int16 R °C ×0.1 Lower outside-temperature limit for heating
IR 534 int16 R °C ×0.1 Lower outside-temperature limit for hot water
IR 535 uint16 R h WPM 3 only
IR 536 int16 R °C ×0.1
IR 537 int16 R °C ×0.1
IR 538 int16 R bar ×0.01
IR 539 int16 R °C ×0.1 WPM 3i only
IR 540 int16 R bar ×0.1 WPM 3i only
IR 541 int16 R bar ×0.1 WPM 3i only
HR 1501 uint16 RW
HR 1502 int16 RW °C ×0.1 Room setpoint for heating
HR 1503 int16 RW °C ×0.1 Room setpoint for heating
HR 1504 int16 RW ×0.01
HR 1505 int16 RW °C ×0.1 Room setpoint for heating
HR 1506 int16 RW °C ×0.1 Room setpoint for heating
HR 1507 int16 RW ×0.01
HR 1509 int16 RW °C ×0.1 Mind the operating limits of the heat pump
HR 1510 int16 RW °C ×0.1
HR 1511 int16 RW °C ×0.1
HR 1512 uint16 RW Mind the number of connected heat pumps
HR 1513 int16 RW °C ×0.1
HR 1514 int16 RW °C ×0.1
HR 1515 int16 RW K ×0.1 Cooling
HR 1516 int16 RW °C ×0.1
HR 1517 int16 RW °C ×0.1
HR 1518 int16 RW K ×0.1
HR 1519 int16 RW °C ×0.1
IR 2501 bool bit 0 R
IR 2501 bool bit 1 R
IR 2501 bool bit 2 R
IR 2501 bool bit 3 R
IR 2501 bool bit 4 R
IR 2501 bool bit 5 R
IR 2501 bool bit 6 R
IR 2501 bool bit 7 R
IR 2501 bool bit 8 R
IR 2501 bool bit 9 R
IR 2501 bool bit 10 R Status word; WPM 3i has no silent mode
IR 2501 bool bit 11 R Status word; WPM 3i has no silent mode
IR 2502 bool bit 0 R
IR 2503 bool bit 0 R WPM 3 only
IR 2503 bool bit 1 R WPM 3 only
IR 2503 bool bit 2 R WPM 3 only
IR 2503 bool bit 3 R WPM 3 only
IR 2503 bool bit 4 R WPM 3 only
IR 2503 bool bit 5 R WPM 3 only
IR 2503 bool bit 6 R WPM 3 only
IR 2503 bool bit 7 R WPM 3 only
IR 2503 bool bit 8 R WPM 3 only
IR 2503 bool bit 9 R WPM 3 only
IR 2503 bool bit 10 R WPM 3 only
IR 2503 bool bit 11 R WPM 3 only
IR 2503 bool bit 12 R WPM 3 only
IR 2503 bool bit 13 R WPM 3 only
IR 2504 uint16 R System fault flag; acknowledge faults only on the ISG service interface
IR 2505 int16 R Zero or negative; the document lists it as unsigned but gives negative values
IR 2506 uint16 R WPM 3 only
IR 2570 uint16 R
IR 2571 uint16 R
IR 2572 uint16 R
IR 2573 uint16 R
IR 3501 uint16 R kWh Daily value
IR 3502 uint16 R kWh Total = MWh part × 1000 + kWh part (kWh part 0-999)
IR 3503 uint16 R MWh Total = MWh part × 1000 + kWh part
IR 3504 uint16 R kWh Daily value
IR 3505 uint16 R kWh Total = MWh part × 1000 + kWh part (kWh part 0-999)
IR 3506 uint16 R MWh Total = MWh part × 1000 + kWh part
IR 3507 uint16 R kWh All heat pumps; total = MWh part × 1000 + kWh part
IR 3508 uint16 R MWh All heat pumps

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