ESPHome Flexit Modbus Server

This project implements a Modbus server for Flexit ventilation systems using ESPHome.
No Flexit CI66 adapter is required.

Note: This is a work in progress and does not yet support all Flexit CS60 sensors or switches.

---

Features

• Control Flexit ventilation systems (tested on CS60, may work with others compatible with CI600 panel)
• Works with ESP8266 or ESP32 microcontrollers
• Integrates with ESPHome for easy Home Assistant support
• No CI66 needed

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Requirements

• Flexit ventilation system with CS60 (or similar) controller
• ESP8266 or ESP32 device
• UART-to-RS485 transceiver (e.g., MAX485, MAX1348)
• Basic ESPHome YAML configuration knowledge

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Recommended Hardware

MCU	RS485 Breakout Board	Notes
XIAO-ESP32-C3	XIAO-RS485-Expansion-Board	Details

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Limitations

• Supply Air Temperature: Can only be set if no CI600 is connected (CS60 limitation).
• Startup Order: ESP must be powered on before CS60, or CS60 won’t poll it.
• Optimistic Settings: Some settings are “optimistic” and may not reflect changes from other panels or servers.
• Address: Address 1 is required for Heater On/Off to function, but this wont work if you have a CI600 connected.

---

Quick Start

1. Connect Hardware:
   Wire your ESP device to the RS485 transceiver and connect to the Flexit controller.

2. ESPHome Configuration:
   Add the following to your ESPHome YAML file (adjust pins and options as needed):

   wifi:
     fast_connect: true           # Needed if powered from the CS60
   
   logger:
     baud_rate: 115200
     hardware_uart: UART1
     level: WARN
   
   external_components:
     - source: github://MSkjel/esphome-flexit-modbus-server@main
       refresh: 60s
       components: 
         - flexit_modbus_server
   
   uart:
     id: modbus_uart
     tx_pin: GPIO1                # Set according to your hardware
     rx_pin: GPIO3                # Set according to your hardware
     baud_rate: 115200
   
   flexit_modbus_server:
     - id: server
       uart_id: modbus_uart
       address: 3 # Address 1 is required for heater on/off, but this wont work in conjuction with a CI600
       # Depending on hardware/optional:
       # tx_enable_pin: GPIO16    # Set according to your hardware.
       # tx_enable_direct: true   # Set according to your hardware. Inverts the DE signal

3. Add Controls and Sensors: You can add switches, buttons, numbers, sensors, etc., using the provided examples. See the full configuration example below for details. You can pick and choose from these sensors/switches.

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Configurations

Full sensor config with extras

This config contains the Flexit sensors and switches and some esphome implemented features. New features might be added here in the future

As of now these are:

• Fireplace mode

globals:
  - id: fireplace_mode_active
    type: bool
    restore_value: no
    initial_value: 'false'

  - id: previous_mode_before_fireplace
    type: int
    restore_value: yes
    initial_value: '2'  # Default to Normal mode if we somehow fail

  - id: fireplace_duration_minutes
    type: int
    restore_value: yes
    initial_value: '60'

  - id: original_supply_fan_max
    type: float
    restore_value: no
    initial_value: '100.0'

  - id: original_extract_fan_max
    type: float
    restore_value: no
    initial_value: '100.0'

  - id: fireplace_supply_fan_speed
    type: int
    restore_value: yes
    initial_value: '90'

  - id: fireplace_extract_fan_speed
    type: int
    restore_value: yes
    initial_value: '20'

    # Track when mode was last changed to debounce conflict detection
  - id: fireplace_mode_change_timestamp
    type: unsigned long
    restore_value: no
    initial_value: '0'

switch:
  - platform: template
    id: heater
    name: "Heater"
    lambda: "return id(server)->read_holding_register(flexit_modbus_server::REG_STATUS_HEATER);"
    turn_on_action:
      - lambda: |-
          id(server)->send_cmd(
            flexit_modbus_server::REG_CMD_HEATER,
            1
          );
    turn_off_action:
      - lambda: |-
          id(server)->send_cmd(
            flexit_modbus_server::REG_CMD_HEATER,
            0
          );

  - platform: template
    id: supply_air_control
    name: "Supply Air Control"
    optimistic: True
    restore_mode: RESTORE_DEFAULT_ON
    turn_on_action:
      - lambda: |-
          id(server)->send_cmd(
            flexit_modbus_server::REG_CMD_TEMPERATURE_SUPPLY_AIR_CONTROL,
            1
          );
    turn_off_action:
      - lambda: |-
          id(server)->send_cmd(
            flexit_modbus_server::REG_CMD_TEMPERATURE_SUPPLY_AIR_CONTROL,
            0
          );

  - platform: template
    name: "Fireplace Mode"
    id: fireplace_mode_switch
    optimistic: false
    lambda: |-
      return id(fireplace_mode_active);

    turn_on_action:
      - lambda: |-
          // Edge case: Don't activate if system is in Stop mode
          int current_mode = id(server)->read_holding_register(flexit_modbus_server::REG_MODE);
          if (current_mode == 0) {
            ESP_LOGW("fireplace", "Cannot activate Fireplace mode while system is stopped");
            return;
          }

          // Save current mode and fan speeds before switching
          id(previous_mode_before_fireplace) = current_mode;

          // Save current Max mode fan speeds (read from the number components)
          id(original_supply_fan_max) = id(supply_air_percentage_max).state;
          id(original_extract_fan_max) = id(extract_air_percentage_max).state;

          ESP_LOGI("fireplace", "Saving current mode: %s (Supply: %.0f%%, Extract: %.0f%%)",
                   flexit_modbus_server::mode_to_string(current_mode).c_str(),
                   id(original_supply_fan_max),
                   id(original_extract_fan_max));

          ESP_LOGI("fireplace", "Activating Fireplace mode");
          id(fireplace_mode_active) = true;

          // Record timestamp BEFORE making changes to prevent false conflict detection
          id(fireplace_mode_change_timestamp) = millis();

      # Set fireplace fan speeds using the existing number components
      - number.set:
          id: supply_air_percentage_max
          value: !lambda "return id(fireplace_supply_fan_speed);"
      - number.set:
          id: extract_air_percentage_max
          value: !lambda "return id(fireplace_extract_fan_speed);"

      - delay: 200ms  # Wait for fan speeds to apply

      # Switch to Max mode using the existing select component
      - select.set:
          id: set_mode
          option: "Max"

      # Start the auto-shutoff timer
      - script.execute: fireplace_timer

      # Update the switch state
      - lambda: |-
          id(fireplace_mode_switch).publish_state(true);

    turn_off_action:
      - script.stop: fireplace_timer
      - lambda: |-
          if (!id(fireplace_mode_active)) {
            ESP_LOGW("fireplace", "Fireplace mode already inactive");
            return;
          }

          ESP_LOGI("fireplace", "Deactivating Fireplace mode");
          id(fireplace_mode_active) = false;

      # Restore original fan speeds using the existing number components
      - number.set:
          id: supply_air_percentage_max
          value: !lambda "return id(original_supply_fan_max);"
      - number.set:
          id: extract_air_percentage_max
          value: !lambda "return id(original_extract_fan_max);"

      - delay: 200ms  # Wait for fan speeds to apply

      # Restore previous mode using the existing select component
      - lambda: |-
          int restore_mode = id(previous_mode_before_fireplace);
          std::string mode_str = flexit_modbus_server::mode_to_string(restore_mode);
          ESP_LOGI("fireplace", "Restoring previous mode: %s", mode_str.c_str());

          // Record timestamp for debouncing conflict detection
          id(fireplace_mode_change_timestamp) = millis();

          auto call = id(set_mode).make_call();
          call.set_option(mode_str);
          call.perform();

      # Update the switch state
      - lambda: |-
          id(fireplace_mode_switch).publish_state(false);

button:
  - platform: template
    id: clear_alarms
    name: "Clear Alarms"
    on_press: 
      - lambda: |-
          id(server)->send_cmd(
            flexit_modbus_server::REG_CMD_CLEAR_ALARMS,
            1
          );

  - platform: template
    id: reset_filter_interval
    name: "Reset Filter Interval"
    on_press: 
      - lambda: |-
          id(server)->send_cmd(
            flexit_modbus_server::REG_CMD_CLEAR_FILTER_ALARM,
            1
          );

  - platform: template
    id: start_max_timer
    name: "Start Max Timer"
    on_press: 
      - lambda: |-
          id(server)->send_cmd(
            flexit_modbus_server::REG_CMD_START_MAX_TIMER,
            1
          );

  - platform: template
    id: stop_max_timer
    name: "Stop Max Timer"
    on_press: 
      - lambda: |-
          id(server)->send_cmd(
            flexit_modbus_server::REG_CMD_STOP_MAX_TIMER,
            1
          );
  
number:
  - platform: template
    id: temperature
    name: "Temperature"
    max_value: 30
    min_value: 10
    step: 0.5
    update_interval: 1s
    lambda: |-
      return id(server)->read_holding_register_temperature(
        flexit_modbus_server::REG_TEMPERATURE_SETPOINT
      );
    set_action:
      lambda: |-
        id(server)->send_cmd(
            flexit_modbus_server::REG_CMD_TEMPERATURE_SETPOINT,
            x * 10
        );

  - platform: template
    id: max_timer_minutes
    name: "Max Timer Minutes"
    max_value: 600
    min_value: 1
    step: 1
    optimistic: True
    restore_value: True
    disabled_by_default: True
    set_action:
      lambda: |-
        id(server)->send_cmd(
            flexit_modbus_server::REG_CMD_MINUTES_MAX_TIMER,
            x
        );

  - platform: template
    id: temperature_supply_min
    name: "Temperature Supply Min"
    max_value: 30
    min_value: 10
    step: 0.5
    optimistic: True
    restore_value: True
    disabled_by_default: True
    mode: BOX
    set_action:
      lambda: |-
        id(server)->send_cmd(
            flexit_modbus_server::REG_CMD_TEMPERATURE_SUPPLY_MIN,
            x * 10
        );

  - platform: template
    id: temperature_supply_max
    name: "Temperature Supply Max"
    max_value: 30
    min_value: 10
    step: 0.5
    optimistic: True
    restore_value: True
    disabled_by_default: True
    mode: BOX
    set_action:
      lambda: |-
        id(server)->send_cmd(
            flexit_modbus_server::REG_CMD_TEMPERATURE_SUPPLY_MAX,
            x * 10
        );

  - platform: template
    id: filter_change_interval
    name: "Filter Change Interval"
    max_value: 360
    min_value: 30
    step: 30
    optimistic: True
    restore_value: True
    mode: BOX
    set_action:
      lambda: |-
        id(server)->send_cmd(
            flexit_modbus_server::REG_CMD_DAYS_FILTER_CHANGE_INTERVAL,
            x
        );

  - platform: template
    id: supply_air_percentage_min
    name: "Supply Air Percentage Min"
    max_value: 100
    min_value: 1
    step: 1
    optimistic: True
    restore_value: True
    disabled_by_default: True
    mode: BOX
    set_action:
      lambda: |-
        id(server)->send_cmd(
            flexit_modbus_server::REG_CMD_PERCENTAGE_SUPPLY_FAN_MIN,
            x
        );
  
  - platform: template
    id: supply_air_percentage_normal
    name: "Supply Air Percentage Normal"
    max_value: 100
    min_value: 1
    step: 1
    optimistic: True
    restore_value: True
    disabled_by_default: True
    mode: BOX
    set_action:
      lambda: |-
        id(server)->send_cmd(
            flexit_modbus_server::REG_CMD_PERCENTAGE_SUPPLY_FAN_NORMAL,
            x
        );
  
  - platform: template
    id: supply_air_percentage_max
    name: "Supply Air Percentage Max"
    max_value: 100
    min_value: 1
    step: 1
    optimistic: True
    restore_value: True
    disabled_by_default: True
    mode: BOX
    set_action:
      lambda: |-
        id(server)->send_cmd(
            flexit_modbus_server::REG_CMD_PERCENTAGE_SUPPLY_FAN_MAX,
            x
        );
  
  - platform: template
    id: extract_air_percentage_min
    name: "Extract Air Percentage Min"
    max_value: 100
    min_value: 1
    step: 1
    optimistic: True
    restore_value: True
    disabled_by_default: True
    mode: BOX
    set_action:
      lambda: |-
        id(server)->send_cmd(
            flexit_modbus_server::REG_CMD_PERCENTAGE_EXTRACT_FAN_MIN,
            x
        );

  - platform: template
    id: extract_air_percentage_normal
    name: "Extract Air Percentage Normal"
    max_value: 100
    min_value: 1
    step: 1
    optimistic: True
    restore_value: True
    disabled_by_default: True
    mode: BOX
    set_action:
      lambda: |-
        id(server)->send_cmd(
            flexit_modbus_server::REG_CMD_PERCENTAGE_EXTRACT_FAN_NORMAL,
            x
        );
  
  - platform: template
    id: extract_air_percentage_max
    name: "Extract Air Percentage Max"
    max_value: 100
    min_value: 1
    step: 1
    optimistic: True
    restore_value: True
    disabled_by_default: True
    mode: BOX
    set_action:
      lambda: |-
        id(server)->send_cmd(
            flexit_modbus_server::REG_CMD_PERCENTAGE_EXTRACT_FAN_MAX,
            x
        );

  - platform: template
    name: "Fireplace Mode Duration"
    id: fireplace_duration
    min_value: 1
    max_value: 240
    step: 1
    unit_of_measurement: "min"
    mode: box
    optimistic: false
    lambda: |-
      return id(fireplace_duration_minutes);
    set_action:
      - lambda: |-
          id(fireplace_duration_minutes) = (int)x;
          ESP_LOGI("fireplace", "Duration set to %d minutes", (int)x);
      - component.update: fireplace_duration

  - platform: template
    name: "Fireplace Supply Fan Speed"
    id: fireplace_supply_speed_control
    min_value: 1
    max_value: 100
    step: 1
    unit_of_measurement: "%"
    mode: box
    optimistic: false
    lambda: |-
      return id(fireplace_supply_fan_speed);
    set_action:
      - lambda: |-
          id(fireplace_supply_fan_speed) = (int)x;
          ESP_LOGI("fireplace", "Fireplace supply fan speed set to %d%%", (int)x);
      - component.update: fireplace_supply_speed_control

  - platform: template
    name: "Fireplace Extract Fan Speed"
    id: fireplace_extract_speed_control
    min_value: 1
    max_value: 100
    step: 1
    unit_of_measurement: "%"
    mode: box
    optimistic: false
    lambda: |-
      return id(fireplace_extract_fan_speed);
    set_action:
      - lambda: |-
          id(fireplace_extract_fan_speed) = (int)x;
          ESP_LOGI("fireplace", "Fireplace extract fan speed set to %d%%", (int)x);
      - component.update: fireplace_extract_speed_control

select:
  - platform: template
    id: set_mode
    name: "Set Mode"
    update_interval: 1s
    lambda: |-
      return flexit_modbus_server::mode_to_string(
        id(server)->read_holding_register(flexit_modbus_server::REG_MODE)
      );
    options:
      - Stop
      - Min
      - Normal
      - Max
    set_action:
      lambda: |-
        id(server)->send_cmd(
            flexit_modbus_server::REG_CMD_MODE,
            flexit_modbus_server::string_to_mode(x)
        );

sensor:
  - platform: template
    id: setpoint_air_temperature
    name: "Setpoint Air Temperature"
    update_interval: 1s
    device_class: temperature
    unit_of_measurement: "°C"
    lambda: |-
      return id(server)->read_holding_register_temperature(
        flexit_modbus_server::REG_TEMPERATURE_SETPOINT
      );

  - platform: template
    id: supply_air_temperature
    name: "Supply Air Temperature"
    update_interval: 60s
    device_class: temperature
    unit_of_measurement: "°C"
    lambda: |-
      return id(server)->read_holding_register_temperature(
        flexit_modbus_server::REG_TEMPERATURE_SUPPLY_AIR
      );
    filters:
      - delta: 0.2

  - platform: template
    id: extract_air_temperature
    name: "Extract Air Temperature"
    update_interval: 60s
    device_class: temperature
    unit_of_measurement: "°C"
    lambda: |-
      return id(server)->read_holding_register_temperature(
        flexit_modbus_server::REG_TEMPERATURE_EXTRACT_AIR
      );
    filters:
      - delta: 0.2

  - platform: template
    id: outdoor_air_temperature
    name: "Outdoor Air Temperature"
    update_interval: 60s
    device_class: temperature
    unit_of_measurement: "°C"
    lambda: |-
      return id(server)->read_holding_register_temperature(
        flexit_modbus_server::REG_TEMPERATURE_OUTDOOR_AIR
      );
    filters:
      - delta: 0.2

  - platform: template
    id: return_water_temperature
    name: "Return Water Temperature"
    update_interval: 60s
    device_class: temperature
    unit_of_measurement: "°C"
    lambda: |-
      return id(server)->read_holding_register_temperature(
        flexit_modbus_server::REG_TEMPERATURE_RETURN_WATER
      );

  - platform: template
    id: heating_percentage
    name: "Heating Percentage"
    update_interval: 20s
    unit_of_measurement: "%"
    lambda: |-
      return id(server)->read_holding_register(
        flexit_modbus_server::REG_PERCENTAGE_HEATING
      );
  
  - platform: template
    id: cooling_percentage
    name: "Cooling Percentage"
    update_interval: 20s
    unit_of_measurement: "%"
    lambda: |-
      return id(server)->read_holding_register(
        flexit_modbus_server::REG_PERCENTAGE_COOLING
      );

  - platform: template
    id: heat_exchanger_percentage
    name: "Heat Exchanger Percentage"
    update_interval: 5s
    unit_of_measurement: "%"
    lambda: |-
      return id(server)->read_holding_register(
        flexit_modbus_server::REG_PERCENTAGE_HEAT_EXCHANGER
      );

  - platform: template
    id: supply_fan_speed_percentage
    name: "Supply Fan Speed Percentage"
    update_interval: 5s
    unit_of_measurement: "%"
    lambda: |-
      return id(server)->read_holding_register(
        flexit_modbus_server::REG_PERCENTAGE_SUPPLY_FAN
      );

  - platform: template
    id: runtime
    name: "Runtime"
    update_interval: 60s
    unit_of_measurement: "h"
    lambda: |-
      return id(server)->read_holding_register_hours(
        flexit_modbus_server::REG_RUNTIME_HIGH
      );

  - platform: template
    id: runtime_normal
    name: "Runtime Normal"
    update_interval: 60s
    unit_of_measurement: "h"
    lambda: |-
      return id(server)->read_holding_register_hours(
        flexit_modbus_server::REG_RUNTIME_NORMAL_HIGH
      );

  - platform: template
    id: runtime_stop
    name: "Runtime Stop"
    update_interval: 60s
    unit_of_measurement: "h"
    lambda: |-
      return id(server)->read_holding_register_hours(
        flexit_modbus_server::REG_RUNTIME_STOP_HIGH
      );

  - platform: template
    id: runtime_min
    name: "Runtime Min"
    update_interval: 60s
    unit_of_measurement: "h"
    lambda: |-
      return id(server)->read_holding_register_hours(
        flexit_modbus_server::REG_RUNTIME_MIN_HIGH
      );

  - platform: template
    id: runtime_max
    name: "Runtime Max"
    update_interval: 60s
    unit_of_measurement: "h"
    lambda: |-
      return id(server)->read_holding_register_hours(
        flexit_modbus_server::REG_RUNTIME_MAX_HIGH
      );

  - platform: template
    id: runtime_rotor
    name: "Runtime Rotor"
    update_interval: 60s
    unit_of_measurement: "h"
    lambda: |-
      return id(server)->read_holding_register_hours(
        flexit_modbus_server::REG_RUNTIME_ROTOR_HIGH
      );

  - platform: template
    id: runtime_heater
    name: "Runtime Heater"
    update_interval: 60s
    unit_of_measurement: "h"
    lambda: |-
      return id(server)->read_holding_register_hours(
        flexit_modbus_server::REG_RUNTIME_HEATER_HIGH
      );

  - platform: template
    id: runtime_filter
    name: "Runtime Filter"
    update_interval: 60s
    unit_of_measurement: "h"
    lambda: |-
      return id(server)->read_holding_register_hours(
        flexit_modbus_server::REG_RUNTIME_FILTER_HIGH
      );

binary_sensor:
  - platform: template
    id: heater_enabled
    name: "Heater Enabled"
    lambda: |-
      return (id(server)->read_holding_register(
        flexit_modbus_server::REG_STATUS_HEATER
      ) != 0);

  - platform: template
    id: alarm_supply_sensor_faulty
    name: "Alarm Supply Sensor Faulty"
    lambda: |-
      return (id(server)->read_holding_register(
        flexit_modbus_server::REG_ALARM_SENSOR_SUPPLY_FAULTY
      ) != 0);

  - platform: template
    id: alarm_extract_sensor_faulty
    name: "Alarm Extract Sensor Faulty"
    lambda: |-
      return (id(server)->read_holding_register(
        flexit_modbus_server::REG_ALARM_SENSOR_EXTRACT_FAULTY
      ) != 0);

  - platform: template
    id: alarm_outdoor_sensor_faulty
    name: "Alarm Outdoor Sensor Faulty"
    lambda: |-
      return (id(server)->read_holding_register(
        flexit_modbus_server::REG_ALARM_SENSOR_OUTDOOR_FAULTY
      ) != 0);

  - platform: template
    id: alarm_return_water_sensor_faulty
    name: "Alarm Return Water Sensor Faulty"
    lambda: |-
      return (id(server)->read_holding_register(
        flexit_modbus_server::REG_ALARM_SENSOR_RETURN_WATER_FAULTY
      ) != 0);

  - platform: template
    id: alarm_overheat_triggered
    name: "Alarm Overheat Triggered"
    lambda: |-
      return (id(server)->read_holding_register(
        flexit_modbus_server::REG_ALARM_SENSOR_OVERHEAT_TRIGGERED
      ) != 0);

  - platform: template
    id: alarm_external_smoke_sensor_triggered
    name: "Alarm External Smoke Sensor Triggered"
    lambda: |-
      return (id(server)->read_holding_register(
        flexit_modbus_server::REG_ALARM_SENSOR_SMOKE_EXTERNAL_TRIGGERED
      ) != 0);

  - platform: template
    id: alarm_water_coil_faulty
    name: "Alarm Water Coil Faulty"
    lambda: |-
      return (id(server)->read_holding_register(
        flexit_modbus_server::REG_ALARM_SENSOR_WATER_COIL_FAULTY
      ) != 0);

  - platform: template
    id: alarm_heat_exchanger_faulty
    name: "Alarm Heat Exchanger Faulty"
    lambda: |-
      return (id(server)->read_holding_register(
        flexit_modbus_server::REG_ALARM_SENSOR_HEAT_EXCHANGER_FAULTY
      ) != 0);

  - platform: template
    id: alarm_filter_change
    name: "Alarm Filter Change"
    lambda: |-
      return (id(server)->read_holding_register(
        flexit_modbus_server::REG_ALARM_FILTER_CHANGE
      ) != 0);

  - platform: template
    name: "Fireplace Mode Conflict Detected"
    id: fireplace_conflict
    internal: true
    lambda: |-
      if (!id(fireplace_mode_active)) {
        return false;
      }

      // Debounce: Allow 5 seconds after mode change for Modbus to propagate
      unsigned long time_since_change = millis() - id(fireplace_mode_change_timestamp);
      if (time_since_change < 10000) {  // 10 second debounce
        return false;  // Too soon after our mode change, ignore
      }

      // Check if mode was manually changed away from Max while fireplace mode is active
      int current_mode = id(server)->read_holding_register(flexit_modbus_server::REG_MODE);
      if (current_mode != 3) {  // Not in Max mode
        ESP_LOGD("fireplace", "Conflict detected: current_mode=%d (expected 3), time_since_change=%lums",
                 current_mode, time_since_change);
        return true;  // Conflict detected
      }
      return false;
    on_press:
      - lambda: |-
          ESP_LOGW("fireplace", "Mode changed manually during Fireplace mode - deactivating");
      - switch.turn_off: fireplace_mode_switch

text_sensor:
  - platform: template
    id: current_mode
    name: "Current Mode"
    update_interval: 1s
    lambda: |-
      return flexit_modbus_server::mode_to_string(
        id(server)->read_holding_register(
          flexit_modbus_server::REG_MODE
        )
      );

script:
  - id: fireplace_timer
    mode: restart
    then:
      - lambda: |-
          int duration = id(fireplace_duration_minutes);
          ESP_LOGI("fireplace", "Starting %d minute timer", duration);
      - delay: !lambda "return id(fireplace_duration_minutes) * 60 * 1000;"
      - lambda: |-
          ESP_LOGI("fireplace", "Fireplace timer expired, deactivating");
      - switch.turn_off: fireplace_mode_switch

Sensors and switches only config

This config contains only the Flexit sensors and switches

switch:
  - platform: template
    name: "Heater"
    lambda: "return id(server)->read_holding_register(flexit_modbus_server::REG_STATUS_HEATER);"
    turn_on_action:
      - lambda: |-
          id(server)->send_cmd(
            flexit_modbus_server::REG_CMD_HEATER,
            1
          );
    turn_off_action:
      - lambda: |-
          id(server)->send_cmd(
            flexit_modbus_server::REG_CMD_HEATER,
            0
          );

  - platform: template
    name: "Supply Air Control"
    optimistic: True
    restore_mode: RESTORE_DEFAULT_ON
    turn_on_action:
      - lambda: |-
          id(server)->send_cmd(
            flexit_modbus_server::REG_CMD_TEMPERATURE_SUPPLY_AIR_CONTROL,
            1
          );
    turn_off_action:
      - lambda: |-
          id(server)->send_cmd(
            flexit_modbus_server::REG_CMD_TEMPERATURE_SUPPLY_AIR_CONTROL,
            0
          );

button:
  - platform: template
    name: "Clear Alarms"
    on_press: 
      - lambda: |-
          id(server)->send_cmd(
            flexit_modbus_server::REG_CMD_CLEAR_ALARMS,
            1
          );

  - platform: template
    name: "Reset Filter Interval"
    on_press: 
      - lambda: |-
          id(server)->send_cmd(
            flexit_modbus_server::REG_CMD_CLEAR_FILTER_ALARM,
            1
          );

  - platform: template
    name: "Start Max Timer"
    on_press: 
      - lambda: |-
          id(server)->send_cmd(
            flexit_modbus_server::REG_CMD_START_MAX_TIMER,
            1
          );

  - platform: template
    name: "Stop Max Timer"
    on_press: 
      - lambda: |-
          id(server)->send_cmd(
            flexit_modbus_server::REG_CMD_STOP_MAX_TIMER,
            1
          );
  
number:
  - platform: template
    name: "Temperature"
    max_value: 30
    min_value: 10
    step: 0.5
    update_interval: 1s
    lambda: |-
      return id(server)->read_holding_register_temperature(
        flexit_modbus_server::REG_TEMPERATURE_SETPOINT
      );
    set_action:
      lambda: |-
        id(server)->send_cmd(
            flexit_modbus_server::REG_CMD_TEMPERATURE_SETPOINT,
            x * 10
        );

  - platform: template
    name: "Max Timer Minutes"
    max_value: 600
    min_value: 1
    step: 1
    optimistic: True
    restore_value: True
    disabled_by_default: True
    set_action:
      lambda: |-
        id(server)->send_cmd(
            flexit_modbus_server::REG_CMD_MINUTES_MAX_TIMER,
            x
        );

  - platform: template
    name: "Temperature Supply Min"
    max_value: 30
    min_value: 10
    step: 0.5
    optimistic: True
    restore_value: True
    disabled_by_default: True
    mode: BOX
    set_action:
      lambda: |-
        id(server)->send_cmd(
            flexit_modbus_server::REG_CMD_TEMPERATURE_SUPPLY_MIN,
            x * 10
        );

  - platform: template
    name: "Temperature Supply Max"
    max_value: 30
    min_value: 10
    step: 0.5
    optimistic: True
    restore_value: True
    disabled_by_default: True
    mode: BOX
    set_action:
      lambda: |-
        id(server)->send_cmd(
            flexit_modbus_server::REG_CMD_TEMPERATURE_SUPPLY_MAX,
            x * 10
        );

  - platform: template
    name: "Filter Change Interval"
    max_value: 360
    min_value: 30
    step: 30
    optimistic: True
    restore_value: True
    mode: BOX
    set_action:
      lambda: |-
        id(server)->send_cmd(
            flexit_modbus_server::REG_CMD_DAYS_FILTER_CHANGE_INTERVAL,
            x
        );

  - platform: template
    name: "Supply Air Percentage Min"
    max_value: 100
    min_value: 1
    step: 1
    optimistic: True
    restore_value: True
    disabled_by_default: True
    mode: BOX
    set_action:
      lambda: |-
        id(server)->send_cmd(
            flexit_modbus_server::REG_CMD_PERCENTAGE_SUPPLY_FAN_MIN,
            x
        );
  
  - platform: template
    name: "Supply Air Percentage Normal"
    max_value: 100
    min_value: 1
    step: 1
    optimistic: True
    restore_value: True
    disabled_by_default: True
    mode: BOX
    set_action:
      lambda: |-
        id(server)->send_cmd(
            flexit_modbus_server::REG_CMD_PERCENTAGE_SUPPLY_FAN_NORMAL,
            x
        );
  
  - platform: template
    name: "Supply Air Percentage Max"
    max_value: 100
    min_value: 1
    step: 1
    optimistic: True
    restore_value: True
    disabled_by_default: True
    mode: BOX
    set_action:
      lambda: |-
        id(server)->send_cmd(
            flexit_modbus_server::REG_CMD_PERCENTAGE_SUPPLY_FAN_MAX,
            x
        );
  
  - platform: template
    name: "Extract Air Percentage Min"
    max_value: 100
    min_value: 1
    step: 1
    optimistic: True
    restore_value: True
    disabled_by_default: True
    mode: BOX
    set_action:
      lambda: |-
        id(server)->send_cmd(
            flexit_modbus_server::REG_CMD_PERCENTAGE_EXTRACT_FAN_MIN,
            x
        );

  - platform: template
    name: "Extract Air Percentage Normal"
    max_value: 100
    min_value: 1
    step: 1
    optimistic: True
    restore_value: True
    disabled_by_default: True
    mode: BOX
    set_action:
      lambda: |-
        id(server)->send_cmd(
            flexit_modbus_server::REG_CMD_PERCENTAGE_EXTRACT_FAN_NORMAL,
            x
        );
  
  - platform: template
    name: "Extract Air Percentage Max"
    max_value: 100
    min_value: 1
    step: 1
    optimistic: True
    restore_value: True
    disabled_by_default: True
    mode: BOX
    set_action:
      lambda: |-
        id(server)->send_cmd(
            flexit_modbus_server::REG_CMD_PERCENTAGE_EXTRACT_FAN_MAX,
            x
        );

select:
  - platform: template
    name: "Set Mode"
    update_interval: 1s
    lambda: |-
      return flexit_modbus_server::mode_to_string(
        id(server)->read_holding_register(flexit_modbus_server::REG_MODE)
      );
    options:
      - Stop
      - Min
      - Normal
      - Max
    set_action:
      lambda: |-
        id(server)->send_cmd(
            flexit_modbus_server::REG_CMD_MODE,
            flexit_modbus_server::string_to_mode(x)
        );

sensor:
  - platform: template
    name: "Setpoint Air Temperature"
    update_interval: 1s
    device_class: temperature
    unit_of_measurement: "°C"
    lambda: |-
      return id(server)->read_holding_register_temperature(
        flexit_modbus_server::REG_TEMPERATURE_SETPOINT
      );

  - platform: template
    name: "Supply Air Temperature"
    update_interval: 60s
    device_class: temperature
    unit_of_measurement: "°C"
    lambda: |-
      return id(server)->read_holding_register_temperature(
        flexit_modbus_server::REG_TEMPERATURE_SUPPLY_AIR
      );
    filters:
      - delta: 0.2

  - platform: template
    name: "Extract Air Temperature"
    update_interval: 60s
    device_class: temperature
    unit_of_measurement: "°C"
    lambda: |-
      return id(server)->read_holding_register_temperature(
        flexit_modbus_server::REG_TEMPERATURE_EXTRACT_AIR
      );
    filters:
      - delta: 0.2

  - platform: template
    name: "Outdoor Air Temperature"
    update_interval: 60s
    device_class: temperature
    unit_of_measurement: "°C"
    lambda: |-
      return id(server)->read_holding_register_temperature(
        flexit_modbus_server::REG_TEMPERATURE_OUTDOOR_AIR
      );
    filters:
      - delta: 0.2

  - platform: template
    name: "Return Water Temperature"
    update_interval: 60s
    device_class: temperature
    unit_of_measurement: "°C"
    lambda: |-
      return id(server)->read_holding_register_temperature(
        flexit_modbus_server::REG_TEMPERATURE_RETURN_WATER
      );

  - platform: template
    name: "Heating Percentage"
    update_interval: 20s
    unit_of_measurement: "%"
    lambda: |-
      return id(server)->read_holding_register(
        flexit_modbus_server::REG_PERCENTAGE_HEATING
      );
  
  - platform: template
    name: "Cooling Percentage"
    update_interval: 20s
    unit_of_measurement: "%"
    lambda: |-
      return id(server)->read_holding_register(
        flexit_modbus_server::REG_PERCENTAGE_COOLING
      );

  - platform: template
    name: "Heat Exchanger Percentage"
    update_interval: 5s
    unit_of_measurement: "%"
    lambda: |-
      return id(server)->read_holding_register(
        flexit_modbus_server::REG_PERCENTAGE_HEAT_EXCHANGER
      );

  - platform: template
    name: "Supply Fan Speed Percentage"
    update_interval: 5s
    unit_of_measurement: "%"
    lambda: |-
      return id(server)->read_holding_register(
        flexit_modbus_server::REG_PERCENTAGE_SUPPLY_FAN
      );

  - platform: template
    name: "Runtime"
    update_interval: 60s
    unit_of_measurement: "h"
    lambda: |-
      return id(server)->read_holding_register_hours(
        flexit_modbus_server::REG_RUNTIME_HIGH
      );

  - platform: template
    name: "Runtime Normal"
    update_interval: 60s
    unit_of_measurement: "h"
    lambda: |-
      return id(server)->read_holding_register_hours(
        flexit_modbus_server::REG_RUNTIME_NORMAL_HIGH
      );

  - platform: template
    name: "Runtime Stop"
    update_interval: 60s
    unit_of_measurement: "h"
    lambda: |-
      return id(server)->read_holding_register_hours(
        flexit_modbus_server::REG_RUNTIME_STOP_HIGH
      );

  - platform: template
    name: "Runtime Min"
    update_interval: 60s
    unit_of_measurement: "h"
    lambda: |-
      return id(server)->read_holding_register_hours(
        flexit_modbus_server::REG_RUNTIME_MIN_HIGH
      );

  - platform: template
    name: "Runtime Max"
    update_interval: 60s
    unit_of_measurement: "h"
    lambda: |-
      return id(server)->read_holding_register_hours(
        flexit_modbus_server::REG_RUNTIME_MAX_HIGH
      );

  - platform: template
    name: "Runtime Rotor"
    update_interval: 60s
    unit_of_measurement: "h"
    lambda: |-
      return id(server)->read_holding_register_hours(
        flexit_modbus_server::REG_RUNTIME_ROTOR_HIGH
      );

  - platform: template
    name: "Runtime Heater"
    update_interval: 60s
    unit_of_measurement: "h"
    lambda: |-
      return id(server)->read_holding_register_hours(
        flexit_modbus_server::REG_RUNTIME_HEATER_HIGH
      );

  - platform: template
    name: "Runtime Filter"
    update_interval: 60s
    unit_of_measurement: "h"
    lambda: |-
      return id(server)->read_holding_register_hours(
        flexit_modbus_server::REG_RUNTIME_FILTER_HIGH
      );

binary_sensor:
  - platform: template
    name: "Heater Enabled"
    lambda: |-
      return (id(server)->read_holding_register(
        flexit_modbus_server::REG_STATUS_HEATER
      ) != 0);

  - platform: template
    name: "Alarm Supply Sensor Faulty"
    lambda: |-
      return (id(server)->read_holding_register(
        flexit_modbus_server::REG_ALARM_SENSOR_SUPPLY_FAULTY
      ) != 0);

  - platform: template
    name: "Alarm Extract Sensor Faulty"
    lambda: |-
      return (id(server)->read_holding_register(
        flexit_modbus_server::REG_ALARM_SENSOR_EXTRACT_FAULTY
      ) != 0);

  - platform: template
    name: "Alarm Outdoor Sensor Faulty"
    lambda: |-
      return (id(server)->read_holding_register(
        flexit_modbus_server::REG_ALARM_SENSOR_OUTDOOR_FAULTY
      ) != 0);

  - platform: template
    name: "Alarm Return Water Sensor Faulty"
    lambda: |-
      return (id(server)->read_holding_register(
        flexit_modbus_server::REG_ALARM_SENSOR_RETURN_WATER_FAULTY
      ) != 0);

  - platform: template
    name: "Alarm Overheat Triggered"
    lambda: |-
      return (id(server)->read_holding_register(
        flexit_modbus_server::REG_ALARM_SENSOR_OVERHEAT_TRIGGERED
      ) != 0);

  - platform: template
    name: "Alarm External Smoke Sensor Triggered"
    lambda: |-
      return (id(server)->read_holding_register(
        flexit_modbus_server::REG_ALARM_SENSOR_SMOKE_EXTERNAL_TRIGGERED
      ) != 0);

  - platform: template
    name: "Alarm Water Coil Faulty"
    lambda: |-
      return (id(server)->read_holding_register(
        flexit_modbus_server::REG_ALARM_SENSOR_WATER_COIL_FAULTY
      ) != 0);

  - platform: template
    name: "Alarm Heat Exchanger Faulty"
    lambda: |-
      return (id(server)->read_holding_register(
        flexit_modbus_server::REG_ALARM_SENSOR_HEAT_EXCHANGER_FAULTY
      ) != 0);

  - platform: template
    name: "Alarm Filter Change"
    lambda: |-
      return (id(server)->read_holding_register(
        flexit_modbus_server::REG_ALARM_FILTER_CHANGE
      ) != 0);

text_sensor:
  - platform: template
    name: "Current Mode"
    update_interval: 1s
    lambda: |-
      return flexit_modbus_server::mode_to_string(
        id(server)->read_holding_register(
          flexit_modbus_server::REG_MODE
        )
      );

---

Optional extras

TCP Bridge

The TCP bridge feature allows you to monitor the Modbus communication over a TCP connection. This is useful for finding new registers.

How It Works

When enabled, the TCP bridge creates a server that:

• Accepts TCP connections on the configured port (default: 502)
• Mirrors all UART data to connected clients in real-time (both TX and RX)
• Sends data with directional framing so you can distinguish between sent and received frames

Frame Protocol

Data is sent to TCP clients using a simple 3-byte header + payload format:

[Direction (1 byte)][Length High (1 byte)][Length Low (1 byte)][Payload (N bytes)]

• Direction: 'T' (0x54) for TX (ESP→UART), 'R' (0x52) for RX (UART→ESP)
• Length: 16-bit big-endian payload length

Configuration Options

Option	Type	Default	Description
tcp_bridge_enabled	boolean	false	Enable/disable TCP bridge
tcp_bridge_port	integer	502	TCP port to listen on
tcp_bridge_max_clients	integer	4	Maximum concurrent clients (1-10)

Example Configuration

flexit_modbus_server:
  - id: server
    uart_id: modbus_uart
    address: 3
    tcp_bridge_enabled: true
    tcp_bridge_port: 8502
    tcp_bridge_max_clients: 2

Monitoring Tool

A Python script for monitoring and decoding the TCP bridge traffic is included in scripts/tcp_bridge_monitor.py.

Features:

• Decodes Modbus RTU frames
• Color-coded TX (ESP→UART) and RX (UART→ESP) traffic
• Track coil state changes with --coil-changes flag

---

TODO

• Add support for more sensors and switches

License

MIT License

---

Credits

• esphome-modbus-server
• modbus-esp8266