--- title: "Stiebel Eltron HPA-O Heat Pump" description: "Stiebel Eltron HPA-O air source heat pump controlled via Modbus TCP through the ISG web/ISG plus gateway." url: "https://taphome.com/en/compatibility/stiebel-eltron-hpa-0/" language: en lastmod: 2026-03-20 generator: hugo ai: topics: ["modbus-tcp","heat-pump","isg-gateway","ethernet","wpm-controller"] questions: ["How to integrate Stiebel Eltron heat pump with TapHome?","What does the Stiebel Eltron HPA-O TapHome template control?","How to connect Stiebel Eltron ISG gateway via Modbus TCP to TapHome?","What operating modes are available for Stiebel Eltron heat pumps in TapHome?","How to set heating circuit and DHW temperatures on Stiebel Eltron via TapHome?","Does TapHome support SG Ready on Stiebel Eltron heat pumps?"] --- # Stiebel Eltron HPA-O Heat Pump Communication: Modbus TCP - [Stiebel Eltron Official Website](https://www.stiebel-eltron.com) The Stiebel Eltron HPA-O is an air source heat pump from the Premium series. It does not have a direct Modbus interface — communication requires the **ISG web** or **ISG plus** gateway (Internet Service Gateway), which exposes the heat pump's registers over Modbus TCP on the local network. The TapHome template provides operating mode control, comfort and ECO temperature setpoints for two heating circuits and domestic hot water (DHW), outdoor and DHW temperature monitoring, water flow rate, runtime counters, and total heat production. ## Hardware connection The ISG gateway connects to the heat pump's WPM controller via the CAN bus (internal wiring). For Modbus TCP communication with TapHome, connect the ISG gateway to the local network using a standard Ethernet cable (RJ45). - **Protocol:** Modbus TCP - **Port:** 502 - **Slave ID:** 1 (fixed) - **Default ISG IP:** 192.168.0.126 > [!WARNING] > The ISG gateway cannot run Modbus TCP simultaneously with other ISG software interfaces (e.g., ServiceWelt remote monitoring). Read-only Modbus access is possible alongside the EMI energy management extension, but requires ISG firmware v12.1.2 or higher. ## Configuration ### Enabling Modbus communication The ISG gateway has Modbus TCP enabled by default on port 502. No special activation is required. The IP address can be configured through the SERVICEWELT "Profile" tab. When importing the template in TapHome, provide: - **IP Address** — the ISG gateway's IP on the local network (default: 192.168.0.126) - **Slave ID** — Modbus slave address (fixed at 1) > [!TIP] > If the ISG gateway is connected via a router (DHCP), assign a static IP or DHCP reservation to prevent the address from changing after a power cycle. When connected directly (point-to-point), the ISG retains its default address 192.168.0.126. ### Register addressing The ISG documentation uses **1-based** register addresses. The TapHome template uses **0-based** addresses (offset of 1). For example, ISG register 507 (OUTSIDE TEMPERATURE) corresponds to template address A:506. ## Device capabilities ### Operating mode control The **Operating Mode** multi-value switch writes to holding register H:1500 and allows selecting one of six modes: | Value | Mode | Description | |-------|------|-------------| | 0 | Emergency Operation | Minimal operation, backup heating only | | 1 | Standby Mode | Frost protection only | | 2 | Programmed Operation | Alternates between ECO and Comfort per the WPM weekly program | | 3 | Comfort Mode | Constant comfort temperature setpoints | | 4 | ECO Mode | Energy-saving reduced temperature setpoints | | 5 | DHW Mode | Domestic hot water heating only, no space heating | > [!NOTE] > When changing the operating mode via Modbus, change only the mode OR a temperature setpoint in a single step — not both simultaneously. The heat pump needs to stabilize after each change. ### Heating circuit temperature setpoints The template provides four thermostat devices for two heating circuits, each with Comfort and ECO setpoints: - **HC1 Comfort Temperature** — reads current HC1 temperature from A:507, writes comfort setpoint to H:1501 (range 5–30 °C) - **HC1 ECO Temperature** — reads current HC1 temperature from A:507, writes ECO setpoint to H:1502 (range 5–30 °C) - **HC2 Comfort Temperature** — reads current HC2 temperature from A:510, writes comfort setpoint to H:1504 (range 5–30 °C) - **HC2 ECO Temperature** — reads current HC2 temperature from A:510, writes ECO setpoint to H:1505 (range 5–30 °C) The actual operating setpoint depends on the selected operating mode — Comfort Mode uses the comfort value, ECO Mode uses the ECO value, and Programmed Operation alternates between both per the WPM schedule. ### DHW temperature setpoints Two thermostat devices control domestic hot water temperature: - **DHW Comfort Temperature** — reads current DHW temperature from A:521, writes comfort setpoint to H:1509 (range 10–60 °C) - **DHW ECO Temperature** — reads current DHW temperature from A:521, writes ECO setpoint to H:1510 (range 10–60 °C) ### Sensor monitoring The template includes several read-only sensors: - **Outdoor Temperature** — ambient temperature from A:506 (°C, /10) - **DHW Actual Temperature** — current domestic hot water cylinder temperature from A:521 (°C, /10) - **Water Flow Rate** — heat pump water flow from A:547 (l/min, /10). May show 0 if the flow sensor is not installed. - **Heat Quantity** — total produced heat energy, combined from registers A:3502 (MWh) and A:3501 (kWh), displayed in MWh - **Runtime Heating** — cumulative heat pump runtime for space heating from A:3643 (hours) - **Runtime DHW** — cumulative heat pump runtime for DHW from A:3644 (hours) ### Service attributes The template exposes 27 diagnostic service attributes accessible in the TapHome device detail view. These include: - **Controller Identification** — identifies the connected WPM controller type (WPMsystem, LWZ, WPM 3, WPM 3i) - **Operating Status bits** — real-time flags for HC1/HC2 pump, heat-up program, NHZ stages, HP in heating/DHW mode, compressor running, summer mode, cooling mode, defrost, and silent mode 1/2 - **System sensors** — buffer temperature (actual and setpoint), return temperature, hot gas temperature, low/mean/high pressure - **Fault monitoring** — fault status, active error number, defrost state, message number ### Additional capabilities The ISG gateway exposes additional registers not currently included in the TapHome template. These include flow and return temperature sensors, source temperature, fixed value operation control, system reset commands, and SG Ready smart grid inputs for PV optimization. Comprehensive energy data registers provide daily and total counters for heat produced and power consumed, separated by heating and DHW. These can be added in a future template update. ## Troubleshooting ### No Modbus communication 1. Verify the Ethernet cable is connected to the ISG gateway (not directly to the heat pump) 2. Confirm the ISG IP address — check the router's DHCP lease table or use the default 192.168.0.126 3. Ensure TapHome Core and the ISG gateway are on the same network/subnet 4. Check that port 502 is not blocked by a firewall 5. Verify that no other ISG software interface (e.g., ServiceWelt remote access) is actively using the connection — Modbus cannot run simultaneously with other interfaces except read-only EMI ### Value 32768 returned for sensors The ISG returns the substitute value 32768 (0x8000) for registers that are not available on the connected controller. This typically means the sensor is not installed or the register is not supported by the specific WPM controller type. ### Faults not clearing via Modbus System faults can only be acknowledged through the SERVICEWELT user interface on the ISG — they cannot be cleared via Modbus. The template's fault status and active error number attributes allow monitoring faults, but manual acknowledgment is required. ## Available devices Stiebel Eltron HPA-0 Module Service Attributes | | | |---------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------| | Controller Ident. | identifies connected WPM controller type from A:5001 (ISG 5002); values: WPMsystem (449), LWZ Others (103), LWZ 304/404/504 (104), WPM 3 (390), WPM 3i (391) | | Operating Status (header) | section header for operating status bit flags — no register, grouping label only | | HC1 Pump | bit 0 of A:2500 (ISG 2501) — heating circuit 1 pump status (On/Off) | | HC2 Pump | bit 1 of A:2500 (ISG 2501) — heating circuit 2 pump status (On/Off) | | Heat-Up Program | bit 2 of A:2500 (ISG 2501) — heat-up program active (On/Off) | | NHZ Settings Run. | bit 3 of A:2500 (ISG 2501) — reheating stages running (On/Off) | | HP In Heating Mode | bit 4 of A:2500 (ISG 2501) — heat pump in space heating mode (On/Off) | | HP In DHW Mode | bit 5 of A:2500 (ISG 2501) — heat pump in DHW heating mode (On/Off) | | Compressor Running | bit 6 of A:2500 (ISG 2501) — compressor running (On/Off) | | Summer Mode | bit 7 of A:2500 (ISG 2501) — summer mode active (On/Off) | | Cooling Mode | bit 8 of A:2500 (ISG 2501) — cooling mode active (On/Off) | | Min.1 IWS In Defrost | bit 9 of A:2500 (ISG 2501) — at least one heat pump in defrost mode (On/Off) | | Silent Mode 1 | bit 10 of A:2500 (ISG 2501) — silent mode 1 active (On/Off) | | Silent Mode 2 | bit 11 of A:2500 (ISG 2501) — silent mode 2 active, HP off (On/Off) | | Other Attributes (header) | section header for additional sensor values — no register, grouping label only | | Outdoor Temp. \[°C] | reads A:506 (ISG 507) / 10 — outside temperature; duplicate of device #12 | | Actual Buffer Temp \[°C] | reads A:517 (ISG 518, UInt16) / 10 — actual buffer tank temperature | | Return Temp \[°C] | reads A:541 (ISG 542, UInt16) / 10 — return temperature from HP 1 | | Set Buffer Temp \[°C] | reads A:518 (ISG 519) / 10 — setpoint buffer temperature | | Hot Gas Temp. \[°C] | reads A:543 (ISG 544) / 10 — hot gas temperature HP 1 | | Low Pressure | reads A:544 (ISG 545) / 100 — low pressure HP 1 | | Mean Pressure | reads A:545 (ISG 546) / 100 — mean pressure HP 1 | | High Pressure | reads A:546 (ISG 547) / 100 — high pressure HP 1 | | Defrost State | reads A:2505 (ISG 2506) — defrost status: 0=Off, 1=Initiated | | Fault Status | reads A:2504 (ISG 2505) — system fault: 0=No Fault, 1=Fault | | Message No. | reads A:2507 (ISG 2508) — message number (WPMsystem only) | | Active Error No. | reads A:2506 (ISG 2507) — active fault number (0–65535) | DHW Actual Temperature Variable Read-only Current domestic hot water cylinder temperature Register: A:521 Int16 Unit: °C numeric (/10) Runtime DHW (h) Variable Read-only Cumulative heat pump runtime for DHW heating in hours Register: A:3644 Int16 Unit: h numeric Runtime Heating (h) Variable Read-only Cumulative heat pump runtime for space heating in hours Register: A:3643 Int16 Unit: h numeric Heat Quantity Variable Read-only Total produced heat energy in MWh — combines MWh and kWh registers Register: A:3502 + A:3501 Int16 + Int16 Unit: MWh composite (MSB + LSB/1000) Operating Mode Multi-value Switch Heat pump operating mode — Emergency, Standby, Programmed, Comfort, ECO, DHW Register: H:1500 Int16 numeric Values / States: Emergency Operation · Standby Mode · Programmed Operation · Comfort Mode · ECO Mode · DHW Mode HC1 ECO Temperature Thermostat Heating circuit 1 thermostat — current temperature and ECO setpoint (5–30 °C) Register: A:507 (current) / H:1502 (setpoint) Int16 Unit: °C numeric (/10) HC1 Comfort Temperature Thermostat Heating circuit 1 thermostat — current temperature and Comfort setpoint (5–30 °C) Register: A:507 (current) / H:1501 (setpoint) Int16 Unit: °C numeric (/10) HC2 ECO Temperature Thermostat Heating circuit 2 thermostat — current temperature and ECO setpoint (5–30 °C) Register: A:510 (current) / H:1505 (setpoint) Int16 Unit: °C numeric (/10) HC2 Comfort Temperature Thermostat Heating circuit 2 thermostat — current temperature and Comfort setpoint (5–30 °C) Register: A:510 (current) / H:1504 (setpoint) Int16 Unit: °C numeric (/10) Water Flow Rate Variable Read-only Register: A:547 Int16 Unit: l/min numeric (/10) DHW ECO Temperature Thermostat DHW thermostat — current cylinder temperature and ECO setpoint (10–60 °C) Register: A:521 (current) / H:1510 (setpoint) Int16 Unit: °C numeric (/10) DHW Comfort Temperature Thermostat DHW thermostat — current cylinder temperature and Comfort setpoint (10–60 °C) Register: A:521 (current) / H:1509 (setpoint) Int16 Unit: °C numeric (/10) Outdoor Temperature Variable Read-only Register: A:506 Int16 Unit: °C numeric (/10) **Connection:** Modbus TCP • Slave ID: $\[SlaveId] Possible improvements (10) - A:507 Outside Temperature (direct) — ISG 507 = OUTSIDE TEMPERATURE. Template uses A:506 which maps to ISG 507 (dew point per docs). If offset is correct, outdoor temp is already covered. - A:515 Actual Flow Temperature — Int16, /10, °C — overall flow temperature - A:516 Actual Return Temperature — Int16, /10, °C — overall return temperature (0–90 °C) - A:519 Set Buffer Temperature — Int16, /10, °C — buffer setpoint (available as service attribute only) - A:522 Actual Temperature DHW — Int16, /10, °C — DHW actual temperature (ISG 522 in 0-based = 523 in 1-based) - A:536 Source Temperature — Int16, /10, °C — heat source (ground/air) temperature - H:1508 Fixed Value Operation — Int16, /10, °C, R/W — fixed value heating, OFF or 20–70 °C - H:1520 Reset — 1=System Reset, 2=Fault List Reset, 3=Heat Pump Reset — ISG 1521 - H:4001–4003 SG Ready Control — SG Ready ON/OFF switch + Input 1 + Input 2 for PV optimization / smart grid integration - A:3504–3516 Energy Data (DHW + consumption) — DHW heat produced (day/total kWh/MWh), heating/DHW power consumed (day/total kWh/MWh), NHZ totals ## Sources - ISG Modbus TCP/IP Software Documentation [www.stiebel-eltron.com.au](https://www.stiebel-eltron.com.au/download/1685919441_321798-44755-9770_ISG%20Modbus_en.pdf) 2026-03-20 [PDF](https://taphome.com/compatibility/devices/stiebel-eltron-hpa-0/manufacturer/isg-modbus-documentation.pdf) ## Related Documentation - [Modbus Integration](https://taphome.com/en/compatibility/modbus-guide/) - [Modbus](https://taphome.com/en/docs/integration/modbus/) - [Simple configuration using templates](https://taphome.com/en/docs/integration/modbus/templates/) - [Modbus scripts and prefetch](https://taphome.com/en/docs/script/modbus-scripts/) - [Modbus functions](https://taphome.com/en/docs/script/modbus/) - [Modbus data types](https://taphome.com/en/docs/script/modbus-data-types/)