Stiebel Eltron WPM (SG Ready)

Installation

1. 1In the ISG Web SERVICEWELT interface, navigate to Settings, then Energy Management, and set SG Activated to ON and SG Ready Input to Modbus to enable Modbus control of the SG Ready inputs.
2. 2Connect the ISG Web to the same LAN as the ModbusCloud Gateway; the ISG listens on TCP port 502 with Slave ID 1 by default. Confirm the ISG IP address under the Profile tab in SERVICEWELT.
3. 3In the ModbusCloud portal, add your ModbusCloud Gateway, then import the Stiebel Eltron WPM (SG Ready) template and assign it to the ISG using the confirmed IP address, port 502, and unit ID 1.
4. 4Verify the connection by reading register 5000 (getmode): a value between 1 and 4 confirms live communication; a value of 32768 (0x8000) indicates an unavailable or misconfigured object.

Things to watch for

01

Register 5000 always returns 32768. What does that mean?

The value 32768 (0x8000) is the ISG substitute value for an unavailable object. This usually means SG Ready is not enabled in the ISG Web interface. Navigate to Settings, Energy Management and set SG Activated to ON and SG Ready Input to Modbus, then retry.

02

The gateway connects but the temperature register shows implausible values.

The WPM temperature registers use a scaling factor of 10: the raw value 203 represents 20.3 degrees. If your dashboard shows values ten times too large, apply a factor-of-0.1 scaling in your channel configuration. Also confirm the ISG addressing offset: ISG addresses are 1-based, so some tools subtract 1 from the documented address.

03

Writing to setmode_a or setmode_b has no visible effect on the heat pump.

Two preconditions must both be met before Modbus writes take effect: SG Ready must be activated in the ISG Web energy management settings, and the WPM must be in programmed-operation mode (Programmbetrieb). Confirm both are set before writing to the holding registers.

04

Is it safe to write any value to the SG Ready setpoint registers at any time?

Write carefully. Sending SG Ready state 4 (maximum heating) for extended periods can push flow temperatures above the heat pump's comfort limits and may affect wear on the compressor. Always validate the target state against your system's operating limits, and restore the default state (2) after a PV surplus event ends.

Registers (4)

2 read / 2 write

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