Why does register 124 always return zero or a fixed value?

Register 124 uses function code 4 (input register) and type int32. Confirm your gateway is polling with FC4, not FC3. Some heat pump firmware versions report temperature in tenths of a degree: if the raw value looks ten times too large, apply a scaling factor of 0.1 in your channel configuration.

The gateway connects but no register values appear at all. What now?

Verify that Modbus TCP is active on the heat pump and that the correct unit ID (default 1) is configured in the portal. Firewalls or managed switches can block port 502. Test connectivity with a Modbus polling tool from the same network segment before troubleshooting the gateway.

Register 72 reads a large unexpected number. Is the byte order wrong?

Register 72 is typed uint32, which spans two 16-bit Modbus registers. If the value looks byte-swapped or word-swapped, toggle the word order setting in your gateway channel configuration. The Xtherma experimental template does not document byte order explicitly, so try both big-endian and little-endian word arrangements.

Can I write a new power limit directly to register 72 from the portal?

Register 72 (setmaxpower) is defined as read-only (FC3, access R) in this template. It reflects the value last written by the connected energy management system, not a setpoint you push from the portal. Do not attempt to write to it without verifying the heat pump manufacturer's documentation: unsupported writes can cause unexpected behaviour or may be silently ignored.

Free Modbus template: Xtherma experimental

Xtherma is a heat pump brand whose experimental Modbus TCP template provides basic integration for solar surplus and energy management platforms. The Xtherma experimental template reads the current operating temperature and the device-internal temperature limit, and surfaces the maximum heating power setpoint written by the controller. These three registers give an energy management system the data it needs to coordinate heat pump operation with available PV surplus. Connecting the Xtherma device to ModbusCloud Gateway over Modbus TCP enables continuous logging and alerting without additional hardware.

Name	Address	Function	Type	Unit	Access
setmaxpower Maximum heating power limit written by the energy management system.	72	FC03	uint32	W	R
temp Current operating temperature reported by the heat pump.	124	FC04	int32	°C	R
limittemp Device-internal temperature limit configured on the heat pump.	51	FC04	int32	°C	R