Controlling LG Heat Pump via Modbus on Home Assistant

I have an LG Therma V heat pump (inside unit: HN0916T.NB1, outside unit: HU091MR.U44) with a 200L DHW (Domestic Hot Water) tank, and I wanted to integrate it with Home Assistant. After some research, I found that the heat pump supports Modbus communication, which opened up a lot of possibilities.

In this post, I'll share how I connected everything and what configuration worked for me.

The Architecture

Here's an overview of my setup:

The data flows like this:

• Modbus ↔ Home Assistant: Two-way communication with the heat pump (reading sensors, sending commands)
• Home Assistant → InfluxDB: Storing historical data for analysis
• Grafana ← InfluxDB: Visualizing the data in dashboards

What is Modbus?

Modbus is an industrial communication protocol that's been around since 1979. It's simple, reliable, and widely used in industrial equipment – including heat pumps.

There are two main types:

• Modbus RTU: Uses serial communication (RS485 wires)
• Modbus TCP: Uses ethernet/IP network

The LG heat pump uses Modbus RTU, but Home Assistant works better with Modbus TCP. To bridge the gap, I needed a Modbus TCP/IP gateway module.

Hardware I Used

Here's what I gathered for this project:

• Ethernet cable – To connect the gateway to my network
• RS485 cable – The communication line between the heat pump and the gateway
• Waveshare RS485 to PoE ETH module – This converts Modbus RTU to Modbus TCP

Making the Connection

Here's how I connected the RS485 cable inside the heat pump's control board:

Home Assistant Configuration

With the hardware in place, I moved on to configuring Home Assistant.

Basic Modbus Connection

I added this to my /homeassistant/configuration.yaml:

modbus:
  - name: "LG Therma V"
    delay: 1
    timeout: 14
    message_wait_milliseconds: 200
    host: "device-ip-address-on-local-lan"
    port: 4196
    type: tcp

Here's what each setting does:

• name: A friendly name for the connection
• delay: Wait time in seconds before the first request
• timeout: How long to wait for a response (14 seconds works well for heat pumps)
• message_wait_milliseconds: Pause between messages to avoid overwhelming the device
• host: The Modbus gateway's IP address (I set a static IP for this)
• port: The TCP port (4196 is the default for Waveshare modules)
• type: TCP connection type

Writing Modbus Queries

To find the correct register addresses, I consulted the LG manual for my model. It lists all the Modbus registers and what data they contain.

Binary Sensors

For monitoring on/off states like whether the pump is running, I configured a binary sensor:

modbus:
  binary_sensors:
    - name: "LG Therma V Pump Running"
      unique_id: "lg_therma_v_pump_running"
      address: 1
      slave: 1
      scan_interval: 20
      device_class: running
      input_type: discrete_input

Key settings:

• address: The Modbus register address from the LG manual
• slave: Set to 1 for single-device setups
• scan_interval: Polling frequency in seconds (20 seconds is reasonable)
• input_type: discrete_input for read-only binary values

Sensors

For reading temperature values, I set up sensors like this one for DHW temperature:

modbus:
  sensors:
    - name: "LG Therma V DHW Temp"
      unique_id: "lg_therma_v_dhw_temperature"
      scale: 0.1
      precision: 1
      scan_interval: 20
      address: 5 # reg 6
      slave: 1
      unit_of_measurement: °C
      device_class: temperature
      input_type: input

Important settings:

• scale: LG reports temperature as integers (e.g., 445 = 44.5°C), so I multiply by 0.1
• precision: Number of decimal places to display
• device_class: Tells Home Assistant this is a temperature sensor
• input_type: input for read-only registers

Switches

To control the heat pump, I configured switches like:

modbus:
  switches:
    - name: "LG Therma V Underflow"
      unique_id: "lg_therma_v_underflow_on_off"
      slave: 1
      address: 0
      write_type: coil
      command_on: 1
      command_off: 0
      verify:
        input_type: coil
        address: 0
        state_on: 1
        state_off: 0

Key settings:

• write_type: coil for boolean writes
• verify: Reads back the state to confirm the command was executed

Climate Entities

For a complete thermostat experience with current temperature and target adjustment, I used a climate entity:

modbus:
  climates:
    - name: "LG Therma V Underflow"
      unique_id: "lg_therma_v_underflow"
      address: 7
      slave: 1
      input_type: input
      max_temp: 33
      min_temp: 16
      offset: 0
      precision: 0
      scale: 0.1
      target_temp_register: 2
      temp_step: 1
      temperature_unit: C
      hvac_mode_register:
        address: 0
        values:
          state_heat: 4

This creates a proper thermostat card in Home Assistant where I can see the current temperature and adjust the target.

Bonus: Recording Data to InfluxDB

I wanted to keep historical data for analysis, so I added InfluxDB to my setup.

What is InfluxDB?

InfluxDB is a time-series database designed specifically for data that changes over time (like temperatures and power consumption). It handles large amounts of time-stamped data efficiently.

Home Assistant + InfluxDB Integration

Home Assistant has built-in support for InfluxDB. I added this to my configuration.yaml:

influxdb:
  api_version: 2
  ssl: false
  host: your-ip
  port: 8086
  token: influxdb-token
  organization: your-org
  bucket: homeassistant
  tags:
    source: HA
  tags_attributes:
    - friendly_name
  default_measurement: units

Configuration notes:

• api_version: Version 2 for modern InfluxDB installations
• ssl: Set to true if using HTTPS
• token: Generated in InfluxDB's web interface
• organization & bucket: These need to be created in InfluxDB first
• tags: Useful for filtering data later

With this configuration, every sensor update in Home Assistant gets automatically logged to InfluxDB.

Grafana: Visualizing the Data

To create dashboards from the stored data, I use Grafana. It connects to InfluxDB and provides flexible visualization options.

Here's my current dashboard:

I can monitor:

• Pump and compressor status
• DHW temperature over time
• Power consumption
• Flow rates
• And more

Setting up Grafana involves:
1. Installing Grafana (I used Docker)
2. Adding InfluxDB as a data source
3. Creating dashboards and panels

Summary

This setup gives me full visibility and control over my LG Therma V heat pump through Home Assistant. I can:

• Monitor temperatures and status in real-time
• Control the heat pump remotely
• Store historical data for analysis
• Visualize everything in Grafana dashboards

The total cost was much lower than LG's official smart home solutions, and I have complete control over my data.

감사합니다 for reading! If you have questions or spot any issues, feel free to leave a comment.