The gateway connects but all register values read zero or timeout.

Confirm that use case 3 or 4 is active in the ONECTA app and that the Modbus protocol is set to TCP/IP. The HomeHub only exposes its Modbus registers when one of these use cases is selected. Also verify the IP address and that port 502 is reachable from the ModbusCloud Gateway on the same LAN segment.

Temperature values from register 42 look wrong or scaled incorrectly.

The HomeHub returns temperature in Temp16 format: read the register as a signed 16-bit integer. The raw value may require dividing by 10 or applying the scaling factor documented in the EKRHH installer reference guide. Check the guide for the exact multiplier applicable to your firmware version.

Why does writing to the SG mode register 55 appear to have no effect?

The Modbus algorithm on the HomeHub is change-based: the unit only acts on a value if it differs from the last written value. If you are writing the same mode code repeatedly, no update is sent to the heat pump. Write a different mode first to force a state transition, then write your target value.

Is it safe to write arbitrary values to setmaxpower (register 56) or setmode (register 55)?

Use caution with write registers. Setting the SG mode to forced-off stops all heat pump operation including frost protection in some configurations. Setting an excessively low power limit via register 56 can prevent the compressor from maintaining minimum running capacity. Always validate the intended value against Daikin's documented range before writing, and test changes during non-critical hours.

Free Modbus template: Daikin HomeHub (SG Ready)

The Daikin HomeHub (model EKRHH) is a DIN-rail gateway accessory that connects Daikin Altherma heat pumps to a building management or energy management system over Modbus TCP. This template reads the active Smart Grid operation mode and current power consumption, and exposes write registers to set the SG mode and cap the maximum power draw. Together these registers let installers integrate Daikin HomeHub installations into demand-response workflows, PV surplus routing, and grid-balancing programs from the ModbusCloud portal with no additional hardware.

Name	Address	Function	Type	Unit	Access
getmode Current Smart Grid operation mode, read from the unit.	55	FC03	int16		R
setmode Smart Grid operation mode setpoint, written to the unit.	55	FC16	int16		W
temp Leaving water or room temperature, signed 16-bit Temp16 format.	42	FC04	int16	°C	R
power Current heat pump power consumption, instantaneous reading.	50	FC04	int16	W	R
setmaxpower Maximum power limit setpoint, caps unit consumption when written.	56	FC16	int16	W	W