Daikin Altherma 4 (SG Ready)

Installation

1. 1Enable Modbus TCP on the Daikin Altherma 4 via the ONECTA app: open Installer settings, select the HomeHub device, choose the SG Ready use case, and set the Modbus protocol to TCP/IP with no encryption on port 502.
2. 2Connect the Daikin HomeHub to the same LAN segment as the ModbusCloud Gateway, ensuring the heat pump's IP address is reachable from the Gateway and that no firewall blocks port 502.
3. 3In the ModbusCloud portal, add a new device, import the Daikin Altherma 4 (SG Ready) template, and enter the HomeHub's IP address together with the configured Modbus unit ID (default 1).
4. 4Verify the connection by reading the getmode register (address 1000) in the portal's live view and confirming the returned value matches the current SG status shown on the HomeHub or ONECTA app.

Things to watch for

01

Why does getmode always return zero even when SG is active?

The Daikin HomeHub uses a change-based Modbus algorithm: the register is only updated when a change is detected. If the unit has not received a new SG command since the last connection, the register may reflect the initial state. Trigger a mode change from the ONECTA app and re-read to confirm communication is working.

02

The gateway connects but no register values appear in the portal. What now?

Check that the Modbus use case selected in the ONECTA app is the SG Ready use case and not use case 1 or 2, which do not expose these registers. Also confirm the port is 502 (no TLS) and that the unit ID matches. The HomeHub allows a maximum of 3 concurrent Modbus TCP connections; if that limit is already reached, new connections are rejected silently.

03

I wrote setmode but the heat pump did not change its behavior. Why?

The HomeHub Modbus is change-based: writing the same value that is already stored will not trigger a command to the unit. Read getmode first, and only write setmode if you are sending a different value. Also confirm that the HomeHub firmware is up to date, as older firmware versions require MMI software version 7.3.0 or higher on the indoor unit.

04

Is it safe to write setmode or setmaxpower from an automated schedule?

Use caution with automated writes to setmode and setmaxpower. Writing an aggressive power limit via setmaxpower applies to the entire system and can interfere with frost protection, domestic hot water schedules, and other protective functions. Always validate the value against the heat pump's operating constraints before writing, and never write setmaxpower to zero unless a forced-off condition is explicitly intended.

Registers (3)

1 read / 2 write

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