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.

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.

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.

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.

Free Modbus template: Daikin Altherma 4 (SG Ready)

The Daikin Altherma 4 (SG Ready) is an air-to-water heat pump designed for residential and light-commercial heating and cooling with Smart Grid integration. This template, communicating over Modbus TCP, covers the three SG Ready registers: the current operation mode (getmode), the writable mode setpoint (setmode), and the Demand Control power cap (setmaxpower). Together these let an energy management system shift or curtail heat pump load in response to grid signals or surplus PV production. The ModbusCloud Gateway makes SG mode and power limit visible and actionable from a single portal without on-site access.

Name	Address	Function	Type	Unit	Access
getmode Current Smart Grid operation mode, read from the heat pump.	•••	•••	•••		R
setmode Smart Grid operation mode setpoint; write to request a new SG mode.	•••	•••	•••		W
setmaxpower Demand Control power limit setpoint; write to cap system power consumption.	•••	•••	•••	W	W

Daikin Altherma 4 (SG Ready)

Overview

Use cases

Installation

Things to watch for

Registers (3)

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Question about your setup?

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