LG Therma V R290 Monobloc (SG Ready)
The LG Therma V R290 Monobloc is an air-to-water heat pump using natural R290 refrigerant, designed for residential and light-commercial space heating, cooling, and domestic hot water production. This template connects via Modbus RTU over RS485 and targets the SG Ready interface: it reads back the current operating mode (getmode, address 9) and a temperature value (temp, address 5), and writes the desired SG Ready mode (setmode, address 9). The result is direct solar-surplus or grid-signal integration from the ModbusCloud portal without any additional controller hardware.
- Protocol
- Modbus RTU
- Connection
- RS485
- Registers
- 3, read and write
- Brand
- LG
- Last updated
Registers (3)
2 read, 1 write
| Name | Unit | Access | Address (Hidden until you enter your email) | Function (hidden) | Type (hidden) |
|---|---|---|---|---|---|
| setmode | Write | ||||
| getmode | Read | ||||
| temp | Read |
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Use cases
- Monitor the current SG Ready operating mode to verify solar-surplus commands are being accepted by the heat pump.
- Track temperature register values over time to detect sensor drift or abnormal operating conditions.
- Alert when the operating mode deviates from an expected SG Ready state during peak tariff windows.
- Compare logged mode transitions against PV generation data to verify solar-to-heat shifting is working.
- Report mode-change history to building owners as evidence of demand-response participation.
Installation
Enable Modbus on the LG Therma V R290 Monobloc by turning on the designated DIP switch inside the outdoor unit, then set the Modbus slave address to 1 via the installer menu on the indoor controller.
Connect the ModbusCloud Gateway to the heat pump RS485 terminals using a shielded twisted-pair cable; configure the Gateway serial port to 9600 bps, 8 data bits, no parity, 1 stop bit.
In your ModbusCloud portal, add the Gateway, import the LG Therma V R290 Monobloc (SG Ready) template, and assign the unit ID that matches the slave address set on the heat pump.
Verify communication by reading the getmode register (address 9, FC3): a value of 0 to 3 confirms a live SG Ready state and that the connection is working correctly.
Things to watch for
Why does reading getmode always return zero or timeout?
First confirm the DIP switch for Modbus communication is turned ON inside the outdoor unit. Also verify the slave address on the heat pump matches the unit ID configured in the portal. The LG Therma V Modbus interface requires the slave address to be set to a non-zero value, and the default may not be 1 on all firmware versions.
The gateway connects but the temp register shows no value. Why?
Register 5 is an input register read with FC4. Confirm your wiring uses the correct RS485 A/B polarity and that the serial parameters are exactly 9600 bps, 8N1. Some RS485 adapters swap A and B lines; swapping them on the heat pump terminal block usually resolves persistent silence.
FC3 and FC4 seem swapped compared to the printed manual. Is that normal?
Yes. A documented quirk of the LG Therma V Modbus implementation is that the manual labels holding registers as FC3 and input registers as FC4, but some firmware revisions invert this in practice. The register addresses in this template follow the corrected mapping as used by the OpenEMS implementation.
Is it safe to write any value to setmode without restriction?
Exercise care when writing to setmode (address 9, FC16). Writing an unsupported or out-of-range mode value may place the heat pump in an unexpected operating state. Always verify the target mode value against the LG installation manual, test with one step at a time, and confirm the readback via getmode before automating repeated writes.
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