Stiebel Eltron LWA/LWZ (SG Ready)

Installation

1. 1Enable Modbus TCP on the Stiebel Eltron ISG: navigate to Settings, then Energy Management, set SG Ready Enabled to ON, and set the SG Ready Input source to Modbus.
2. 2Connect the ISG to the same LAN segment as the ModbusCloud Gateway using a standard Ethernet cable; confirm the ISG has a reachable IP address on port 502.
3. 3In the ModbusCloud portal, add a new device, import the Stiebel Eltron LWA/LWZ (SG Ready) template, and assign the correct unit ID (default 1) together with the ISG IP address.
4. 4Verify the connection by reading the getmode register (address 5000); a value of 1, 2, 3, or 4 confirms a live response. If 32768 is returned, the register is unavailable on this ISG firmware version.

Things to watch for

01

The getmode register always returns 32768. What does that mean?

The value 32768 (0x8000) is the Stiebel Eltron substitute value for an unavailable register. This typically means the ISG firmware does not expose the SG Ready block, or the Modbus TCP interface is not fully activated. Update the ISG to the latest firmware and confirm the Modbus TCP/IP interface appears in the ISG interface list.

02

Writes to setmode_b have no effect on the heat pump.

SG Ready Modbus control requires a two-step write: setmode_a (address 4001) must be written with value 1 to enable Modbus control before setmode_b (address 4002) is evaluated. Also confirm that SG Ready Enabled is set to ON and the SG Ready Input is set to Modbus in the ISG Energy Management menu.

03

Why can the gateway connect to the ISG but no registers are readable?

The ISG uses 1-based addressing. Some Modbus clients subtract 1 automatically, which can shift addresses off by one. Verify your client is sending the exact addresses listed in the template (5000 for getmode, 4001 and 4002 for setmode). Also confirm port 502 is not blocked by a firewall on the ISG or local network.

04

Is it safe to write setmode_b freely to shift the heat pump into forced mode?

Exercise caution: forced operating mode (SG Ready state 3 or 4) causes the heat pump to run at elevated targets that may exceed DHW or heating circuit limits set on the heat pump manager. Prolonged forced operation can trigger safety cutouts. Always test with short write intervals first and verify that return to normal mode (state 2) is confirmed via getmode before repeating.

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