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.
- Protocol
- Modbus TCP
- Connection
- Ethernet, Modbus TCP
- Registers
- 3, read only
- Brand
- Xtherma
- Last updated
Registers (3)
3 read, 0 write
| Name | Unit | Access | Address (Hidden until you enter your email) | Function (hidden) | Type (hidden) |
|---|---|---|---|---|---|
| setmaxpower | W | Read | |||
| temp | °C | Read | |||
| limittemp | °C | Read |
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If a device is not in the library yet, we build the template for free as soon as we have the register data.
Use cases
- Monitor the current operating temperature over time to verify the heat pump responds correctly to power adjustments.
- Track the device-internal temperature limit to confirm it remains within the range set during commissioning.
- Alert when the reported temperature deviates significantly from the expected setpoint during heating periods.
- Verify that the maximum power value is being updated at the expected interval by the energy management controller.
- Compare temperature readings before and after maintenance visits to detect sensor drift or calibration shifts.
Installation
Enable Modbus TCP on the Xtherma heat pump under the communication or energy management section of its control interface, and note the assigned unit ID (typically 1).
Connect the heat pump to the same local network as the ModbusCloud Gateway using a standard Ethernet cable and confirm the device is reachable on port 502.
In the ModbusCloud portal, add the Gateway, import the Xtherma experimental template, and set the unit ID and IP address to match the heat pump's network configuration.
Spot-check register 124 (temp) in the live register view of your portal and confirm the value matches the temperature shown on the heat pump's own display.
Things to watch for
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.
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