Controlling an LG Therma V Heat Pump + Daikin Fancoils with Modbus, IR Blasters, and Home Assistant

Table of Contents

The System
#

My house runs on an LG Therma V air-to-water heat pump. It heats or cools water that circulates through 5 Daikin fancoil units — wall-mounted units in the living room, hallway, and three bedrooms across two floors.

The problem: these are all separate, disconnected systems. The heat pump has its own controller. Each fancoil has its own IR remote. Nothing talks to anything else. If you turn on the heat pump but forget to switch on the fancoils, you’re heating water that nobody uses. If you turn off the pump but leave the fancoils running, they blow room-temperature air.

I wanted one system that coordinates everything. No more walking around the house with 5 different remotes. No more forgetting to turn on a fancoil in the bedroom. One button to turn on the climate, one button to turn it off — and ideally, one that doesn’t blow cold air at me while the pump is still warming up.

The Three Integration Layers
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Layer 1: LG Therma V via Modbus TCP
#

The Therma V has a Modbus port on its PCB, but it doesn’t speak TCP natively. To bridge it to the network, I use an el-cheapo BOROCO Protoss Modbus to TCP converter (based on the HF-PE11 chipset) — a small box that connects to the heat pump’s Modbus port via a UTP cable running from the electrical panel to the outdoor unit, and exposes it as Modbus TCP on port 8899 over WiFi. From there, Home Assistant’s built-in Modbus integration connects directly — no cloud, no proprietary gateway, pure local control.

The Elfin EW11A converter connected to the LG Therma V heat pump

UTP cable connection from the converter to the heat pump’s Modbus port on the PCB

What I get from Modbus:

Register	Sensor	Use
Discrete input 1	Pump status	Is the pump running?
Discrete input 3	Compressor status	Is the compressor active?
Input register 2	Inlet temperature	Water returning from fancoils
Input register 12	Outdoor air temp	For heating/cooling mode detection
Holding register 2	Target temperature	Read/write setpoint
Holding register 4	AI shift	Fine-tune the AI control offset
Coil 0	Power on/off	Start/stop the heat pump
Coil 2	Silent mode	Toggle quiet operation

Plus compressor RPM, evaporator/compressor pressure, flow rate, defrost status, error status, and DHW (hot water) status. Full visibility into the heat pump’s internals.

LG Therma V dashboard — all Modbus sensors, real-time COP, production vs consumption charts, room temperature equilibrium, compressor RPM, and condensation safety margins

The Modbus Two’s Complement Trick
#

The AI shift register (holding register 4) supports negative values (-5 to +5°C offset). But Modbus registers are unsigned 16-bit integers. Negative values are stored as two’s complement — so -3 becomes 65533.

Reading it back into HA requires the reverse conversion:

# Modbus → HA slider (unsigned to signed)
value: >-
  {% set raw = states('sensor.lg_therma_ai_shift_raw') | int(0) %}
  {% if raw > 32767 %}
    {{ raw - 65536 }}
  {% else %}
    {{ raw }}
  {% endif %}

# HA slider → Modbus (signed to unsigned)
value: >-
  {% set val = states('input_number.lg_ai_shift') | int(0) %}
  {% if val < 0 %}
    {{ val + 65536 }}
  {% else %}
    {{ val }}
  {% endif %}

Two automations keep the HA slider and the Modbus register in bidirectional sync, with guards to prevent feedback loops.

Layer 2: Daikin Fancoils via Broadlink IR + SmartIR
#

The 5 Daikin fancoil units have no network connectivity — only IR remotes. The solution: Broadlink RM4 IR blasters, one per room (5 total: 3× RM4 mini, 2× RM4 pro), paired with the SmartIR custom component.

Broadlink devices in Home Assistant — 5 IR blasters, one per room

SmartIR turns each Broadlink + fancoil combination into a proper climate entity in HA — with temperature control, fan modes, and HVAC modes. It works by storing a database of IR codes and sending the right one for each state combination.

The hard part: learning the IR codes. My Daikin fancoils weren’t in SmartIR’s device database. I had to learn every IR code manually — pressing each button combination on the physical remote while the Broadlink recorded the signal. Every temperature step, every fan speed, every mode. Then I contributed the codes back to the project:

SmartIR PR #1162 — Daikin fancoil support

The SmartIR config for each fancoil looks like this:

climate:
  - platform: smartir
    name: Living Room AC
    unique_id: living_room_ac
    device_code: 3241
    controller_data: remote.rf_living_room
    temperature_sensor: sensor.rf_living_room_temperature
    humidity_sensor: sensor.rf_living_room_humidity
    power_sensor: switch.shelly_rack_switch_1
    power_sensor_restore_state: true

Each Broadlink also has a built-in temperature and humidity sensor — which SmartIR uses for the climate entity’s current readings.

Layer 3: Climate Groups
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With 5 individual climate entities, controlling the house means tapping 5 different cards. The climate_group custom component solves this — it groups multiple climate entities into a single virtual thermostat:

climate:
  - platform: climate_group
    name: 'Climate Group Downstairs'
    temperature_unit: C
    entities:
      - climate.saloni_ac
      - climate.khol_ac
      - climate.kato_domatio_ac

  - platform: climate_group
    name: 'Climate Group Upstairs'
    temperature_unit: C
    entities:
      - climate.pano_megalo_domatio_ac
      - climate.pano_mikro_domatio_ac

Set the temperature on the group → all fancoils in that group follow. One control per floor.

The daily control — heat pump thermostat, AI shift slider, and the two fancoil groups (downstairs 19.9°C, upstairs 21.3°C)

Climate Group Downstairs — one thermostat controlling Living Room AC, Hall AC, and Bedroom AC simultaneously

Climate Group Upstairs — one thermostat controlling both bedroom fancoils, with current temperature 21.2°C and target 22°C

Each climate group shows the individual fancoils underneath — you can see exactly which units are part of the group and their current state. Set the temperature on the group, and all units follow. The family sees two thermostats, not five remotes.

Hardware Layer: Shelly Pro 4PM for Power Control
#

The fancoils are powered through a Shelly Pro 4PM in the electrical panel — two channels, one for the downstairs circuit and one for upstairs. This gives us two things: a hard on/off switch that the automations use to start and stop the fancoils, and per-circuit power monitoring so we can track exactly how much energy the HVAC system consumes.

Shelly Pro 4PM closeup — 4 channels: A/C Rooms, A/C Saloni, Thermosifonas, Tablet. Next to it, the Hager ESC225 contactor

The full electrical panel — Shelly Pro 4PM and Shelly 1PM at the bottom row, LG Therma V controller on the left, and a wall-mounted HA dashboard tablet showing the whole system at a glance

The Automation: Don’t Blow Cold Air
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This is the automation that ties everything together. The problem it solves: when the heat pump starts, the water needs several minutes to reach the target temperature. If the fancoils start immediately, they blow cold (or warm) air until the water is ready.

Start Fancoils Only When Water is Ready
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The automation checks every minute. After the pump has been on for at least 4 minutes, it evaluates whether the water temperature has reached the setpoint — but it needs to know whether the system is heating or cooling to compare correctly:

# Mode detection from outdoor temperature
{% if outside > 25 %}
  {% set mode = 'cooling' %}
{% elif outside < 15 %}
  {% set mode = 'heating' %}
{% else %}
  # Grey zone: use delta-T between outlet and inlet
  {% set d = outlet - inlet %}
  {% if d > 0.4 %}
    {% set mode = 'heating' %}
  {% elif d < -0.4 %}
    {% set mode = 'cooling' %}
  {% else %}
    {% set mode = 'unknown' %}
  {% endif %}
{% endif %}

# Ready check based on produced water temperature
{% if mode == 'cooling' %}
  {{ outlet <= (setpoint + 0.5) }}
{% elif mode == 'heating' %}
  {{ outlet >= (setpoint - 0.5) }}
{% endif %}

The 15-25°C grey zone is tricky — outdoor temperature alone doesn’t tell you if you’re heating or cooling. The fallback uses the delta-T between outlet and inlet water: if outlet is warmer than inlet, you’re heating; if cooler, you’re cooling.

When the water is ready → turn on the Shelly relays that power the fancoil circuit → Telegram notification.

Stop Fancoils When Pump Stops
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When the pump turns off, the automation waits 4 minutes (to use the remaining heated/cooled water) then turns off the fancoil relays. The stop sequence includes a quirky on-off-on-off power cycle — this resets the fancoil valve state so they don’t get stuck in an intermediate position.

The Result
#

The whole system works as one unit now:

Turn on the heat pump (from HA, physical switch, or schedule)
Wait for water to reach temperature — fancoils stay off, no cold air
Fancoils start automatically — Telegram notification confirms
Control per floor via climate groups — one slider per floor
Turn off the pump → fancoils stop automatically after 4 minutes

No more forgetting to turn on fancoils. No more cold air blasts. No more leaving fancoils running after the pump is off.

The Broadlink IR blasters give full climate control over units that were never designed to be smart. The Modbus connection gives deep visibility into the heat pump’s state. And the climate groups make it manageable for the rest of the family — they see two thermostats (upstairs, downstairs), not five individual units.

Appendix: Fancoil Automations + AI Shift Sync
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Click to expand — Start Fancoils When Water is Ready

alias: "Heat Pump — Start Fancoils When Ready"
triggers:
  - minutes: /1
    trigger: time_pattern

conditions:
  # Pump has been on for at least 4 minutes
  - condition: state
    entity_id: switch.lg_therma_power
    state: "on"
    for:
      minutes: 4

  # At least one fancoil relay is off
  - condition: or
    conditions:
      - condition: state
        entity_id: switch.fancoil_relay_downstairs
        state: "off"
      - condition: state
        entity_id: switch.fancoil_relay_upstairs
        state: "off"

  # Water temperature has reached setpoint (mode-aware)
  - condition: template
    value_template: >-
      {% set outside  = states('sensor.lg_therma_outdoor_air_temp') | float(0) %}
      {% set outlet   = states('sensor.lg_therma_outlet_temp') | float(0) %}
      {% set inlet    = states('sensor.lg_therma_inlet_temp') | float(0) %}
      {% set setpoint = state_attr('climate.lg_therma_climate_control','temperature') | float(0) %}
      {% set band     = 0.5 %}
      {% set dt_band  = 0.4 %}

      {# Mode detection #}
      {% if outside > 25 %}
        {% set mode = 'cooling' %}
      {% elif outside < 15 %}
        {% set mode = 'heating' %}
      {% else %}
        {% set d = outlet - inlet %}
        {% if d > dt_band %}
          {% set mode = 'heating' %}
        {% elif d < -dt_band %}
          {% set mode = 'cooling' %}
        {% else %}
          {% set mode = 'unknown' %}
        {% endif %}
      {% endif %}

      {# Ready check #}
      {% if mode == 'cooling' %}
        {{ outlet <= (setpoint + band) }}
      {% elif mode == 'heating' %}
        {{ outlet >= (setpoint - band) }}
      {% else %}
        false
      {% endif %}

actions:
  - action: switch.turn_on
    target:
      entity_id:
        - switch.fancoil_relay_downstairs
        - switch.fancoil_relay_upstairs
  - action: notify.send_message
    target:
      entity_id: notify.your_telegram_bot
    data:
      title: "Heat Pump"
      message: "Water reached temperature. Fancoils ON."

mode: single

Click to expand — Stop Fancoils When Pump Stops

alias: "Heat Pump — Stop Fancoils"
triggers:
  - minutes: /1
    trigger: time_pattern

conditions:
  # Pump has been off for at least 4 minutes
  - condition: state
    entity_id: switch.lg_therma_power
    state: "off"
    for:
      minutes: 4

  # At least one fancoil relay is still on
  - condition: or
    conditions:
      - condition: state
        entity_id: switch.fancoil_relay_downstairs
        state: "on"
      - condition: state
        entity_id: switch.fancoil_relay_upstairs
        state: "on"

actions:
  - action: notify.send_message
    target:
      entity_id: notify.your_telegram_bot
    data:
      title: "Heat Pump"
      message: "Pump stopped. Turning off fancoils."

  # Turn off
  - action: switch.turn_off
    target:
      entity_id:
        - switch.fancoil_relay_downstairs
        - switch.fancoil_relay_upstairs

  # Valve reset cycle (on-off-on-off to prevent stuck valves)
  - delay: "00:00:10"
  - action: switch.turn_on
    target:
      entity_id:
        - switch.fancoil_relay_downstairs
        - switch.fancoil_relay_upstairs
  - delay: "00:00:06"
  - action: switch.turn_off
    target:
      entity_id:
        - switch.fancoil_relay_downstairs
        - switch.fancoil_relay_upstairs

mode: single

Click to expand — Enforce AI Control on HA Startup

alias: "Therma V — Enforce AI Control on Startup"
triggers:
  - event: start
    trigger: homeassistant

actions:
  # Write register 1 = 514 to force AI control mode
  - action: modbus.write_register
    data:
      hub: "Heat Pump - LG Therma V"
      slave: 1
      address: 1
      value: 514

mode: single

Click to expand — AI Shift Bidirectional Sync (HA slider ↔ Modbus)

# --- HA Slider → Modbus ---
alias: "LG Therma AI Shift to Modbus"
triggers:
  - platform: state
    entity_id: input_number.lg_ai_shift

conditions:
  - condition: template
    value_template: >-
      {% set slider = states('input_number.lg_ai_shift') | int(0) %}
      {% set raw_str = states('sensor.lg_therma_ai_shift_raw') %}
      {% if raw_str in ['unknown', 'unavailable'] %}
        true
      {% else %}
        {% set raw = raw_str | int(0) %}
        {% if raw > 32767 %}{% set raw = raw - 65536 %}{% endif %}
        {{ slider != raw }}
      {% endif %}

actions:
  - action: modbus.write_register
    data:
      hub: "Heat Pump - LG Therma V"
      address: 4
      unit: 1
      value: >-
        {% set val = states('input_number.lg_ai_shift') | int(0) %}
        {% if val < 0 %}{{ val + 65536 }}{% else %}{{ val }}{% endif %}

mode: single

# --- Modbus → HA Slider ---
alias: "LG Therma AI Shift from Modbus"
triggers:
  - platform: state
    entity_id: sensor.lg_therma_ai_shift_raw

conditions:
  - condition: template
    value_template: >-
      {{ states('sensor.lg_therma_ai_shift_raw') not in ['unknown', 'unavailable'] }}

actions:
  - action: input_number.set_value
    data:
      entity_id: input_number.lg_ai_shift
      value: >-
        {% set raw = states('sensor.lg_therma_ai_shift_raw') | int(0) %}
        {% if raw > 32767 %}{{ raw - 65536 }}{% else %}{{ raw }}{% endif %}

mode: single

Appendix: Full Modbus Configuration for LG Therma V
#

Click to expand — LG Therma V Modbus YAML

modbus:
  - name: "Heat Pump - LG Therma V"
    delay: 1
    timeout: 14
    message_wait_milliseconds: 200
    host: YOUR_HEAT_PUMP_IP
    port: 8899
    type: tcp

    binary_sensors:
      - name: "lg_therma_heating_mode"
        address: 0
        scan_interval: 60
        slave: 1
        input_type: coil

      - name: "lg_therma_flow_too_low"
        address: 0
        scan_interval: 60
        slave: 1
        input_type: discrete_input

      - name: "lg_therma_pump_status"
        address: 1
        scan_interval: 10
        slave: 1
        input_type: discrete_input
        device_class: running

      - name: "lg_therma_compressor_status"
        address: 3
        scan_interval: 10
        slave: 1
        input_type: discrete_input
        device_class: running

      - name: "lg_therma_defrost_status"
        address: 4
        scan_interval: 60
        slave: 1
        input_type: discrete_input
        device_class: running

      - name: "lg_therma_dhw_status"
        address: 5
        scan_interval: 60
        slave: 1
        input_type: discrete_input
        device_class: running

      - name: "lg_therma_disinfect_status"
        address: 6
        scan_interval: 60
        slave: 1
        input_type: discrete_input
        device_class: running

      - name: "lg_therma_silent_status"
        address: 7
        scan_interval: 10
        slave: 1
        input_type: discrete_input

      - name: "lg_therma_error_status"
        address: 13
        scan_interval: 60
        slave: 1
        input_type: discrete_input
        device_class: problem

    sensors:
      - name: "lg_therma_inlet_temp"
        unique_id: "lg_therma_inlet_temp"
        scan_interval: 10
        address: 2
        slave: 1
        input_type: input
        scale: 0.1
        device_class: temperature
        unit_of_measurement: "°C"
        precision: 1

      - name: "lg_therma_flow_rate"
        unique_id: "lg_therma_flow_rate"
        scan_interval: 10
        address: 8
        slave: 1
        input_type: input
        scale: 0.1
        unit_of_measurement: "l/min"
        precision: 1

      - name: "lg_therma_outdoor_air_temp"
        unique_id: "lg_therma_outdoor_air_temp"
        scan_interval: 10
        address: 12
        slave: 1
        input_type: input
        scale: 0.1
        device_class: temperature
        unit_of_measurement: "°C"
        precision: 1

      - name: "lg_therma_compressor_rpm"
        unique_id: "lg_therma_compressor_rpm"
        scale: 60
        precision: 0.1
        scan_interval: 10
        address: 24
        slave: 1
        unit_of_measurement: rpm
        input_type: input

      - name: "lg_therma_evaporator_pressure"
        unique_id: "lg_therma_evaporator_pressure"
        address: 23
        scan_interval: 60
        unit_of_measurement: Bar
        slave: 1
        input_type: input
        scale: 0.01

      - name: "lg_therma_compressor_pressure"
        unique_id: "lg_therma_compressor_pressure"
        address: 22
        scan_interval: 60
        unit_of_measurement: Bar
        slave: 1
        input_type: input
        scale: 0.01

      - name: "lg_therma_ai_shift_raw"
        unique_id: "lg_therma_ai_shift_raw"
        address: 4
        slave: 1
        input_type: holding
        scan_interval: 4

    switches:
      - name: "lg_therma_power"
        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

      - name: "lg_therma_silent_mode"
        slave: 1
        address: 2
        write_type: coil
        command_on: 1
        command_off: 0
        verify:
          input_type: coil
          address: 2
          state_on: 1
          state_off: 0

    climates:
      - name: "lg_therma_climate_control"
        address: 3
        slave: 1
        input_type: input
        max_temp: 50
        min_temp: 5
        offset: 0
        precision: 1
        scale: 0.1
        target_temp_register: 2
        temp_step: 1
        temperature_unit: C
        write_registers: true
        hvac_mode_register:
          address: 0
          values:
            state_cool: 0
            state_auto: 3
            state_heat: 4

The System#

The Three Integration Layers#

Layer 1: LG Therma V via Modbus TCP#

The Modbus Two’s Complement Trick#

Layer 2: Daikin Fancoils via Broadlink IR + SmartIR#

Layer 3: Climate Groups#

Hardware Layer: Shelly Pro 4PM for Power Control#

The Automation: Don’t Blow Cold Air#

Start Fancoils Only When Water is Ready#

Stop Fancoils When Pump Stops#

The Result#

Appendix: Fancoil Automations + AI Shift Sync#

Appendix: Full Modbus Configuration for LG Therma V#

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