Code of a device, created with ESPHome, to integrate an OpenTherm boiler with Home Assistant

opentherm.yaml

substitutions:
  devicename: opentherm
  upper_devicename: Opentherm

esphome:
  name: $devicename
  platform: ESP8266
  board: d1_mini_lite
  arduino_version: '2.7.2'  
  platformio_options:
    lib_deps: 
    - ihormelnyk/OpenTherm Library @ 1.1.0
    - ESP Async WebServer

  includes:
    - opentherm_component.h
    - opentherm_climate.h
    - opentherm_switch.h
    - opentherm_binary.h

wifi:
  ssid: !secret wifi_name
  password: !secret wifi_password
  
# Enable logging
logger:
  baud_rate: 74880
  #level: DEBUG

api:

ota:

custom_component:
  - lambda: |-
      auto opentherm = new OpenthermComponent();
      return {opentherm};
    
    components:
      - id: opentherm

sensor:
  - platform: custom
    lambda: |-    
      OpenthermComponent *openthermComp = (OpenthermComponent*) opentherm;
      return { 
        openthermComp->boiler_temperature, 
        openthermComp->external_temperature_sensor, 
        openthermComp->return_temperature_sensor, 
        openthermComp->pressure_sensor,
        openthermComp->modulation_sensor
      };
    sensors:
    - name: "Boiler Temperature"
      unit_of_measurement: °C
      accuracy_decimals: 2  
    - name: "External Temperature"
      unit_of_measurement: °C
      accuracy_decimals: 0  
    - name: "Return Temperature"
      unit_of_measurement: °C
      accuracy_decimals: 2
    - name: "Heating Water Pressure"
      unit_of_measurement: hPa
      accuracy_decimals: 2
    - name: "Boiler Modulation"
      unit_of_measurement: "%"
      accuracy_decimals: 0

binary_sensor:
  - platform: custom
    lambda: |-
      OpenthermComponent *openthermComp = (OpenthermComponent*) opentherm;
      return {openthermComp->flame};

    binary_sensors:
    - name: "Flame"
      #device_class: heat

switch:
  - platform: custom
    lambda: |-
      OpenthermComponent *openthermComp = (OpenthermComponent*) opentherm;
      return {openthermComp->thermostatSwitch};

    switches:
      name: "Termostato ambiente"

climate:
  - platform: custom
    lambda: |-
      OpenthermComponent *openthermComp = (OpenthermComponent*) opentherm;
      return {
        openthermComp->hotWaterClimate, 
        openthermComp->heatingWaterClimate
      };

    climates:
      - name: "Hot water"
      - name: "Heating water"

opentherm_binary.h

#pragma once

#include "esphome.h"

class OpenthermBinarySensor : public BinarySensor {
};

opentherm_climate.h

#pragma once
#include "esphome.h"


class OpenthermClimate : public Climate {
private:
    const char *TAG = "opentherm_climate";
public:

    climate::ClimateTraits traits() override {

        auto traits = climate::ClimateTraits();
        traits.set_supports_current_temperature(true);
        traits.set_supports_auto_mode(false);
        traits.set_supports_cool_mode(false);
        traits.set_supports_heat_mode(true);
        traits.set_supports_two_point_target_temperature(false);
        traits.set_supports_away(false);
        traits.set_supports_action(true);

        traits.set_visual_min_temperature(5);
        traits.set_visual_max_temperature(80);
        traits.set_visual_temperature_step(1);

        return traits;    
    }

  void control(const ClimateCall &call) override {

    if (call.get_mode().has_value()) {
        // User requested mode change
        ClimateMode mode = *call.get_mode();
        // Send mode to hardware
        // ...
        ESP_LOGD(TAG, "get_mode");    

        // Publish updated state
        this->mode = mode;
        this->publish_state();
    }
    if (call.get_target_temperature().has_value()) {
        // User requested target temperature change
        float temp = *call.get_target_temperature();
        // Send target temp to climate
        // ...
        ESP_LOGD(TAG, "get_target_temperature");    

        this->target_temperature = temp;
        this->publish_state();
    }

  }
};

opentherm_component.h

#include "esphome.h"
#include "esphome/components/sensor/sensor.h"
#include "OpenTherm.h"
#include "opentherm_switch.h"
#include "opentherm_climate.h"
#include "opentherm_binary.h"


// Pins to OpenTherm Adapter
const int inPin = D5; 
const int outPin = D6; 

OpenTherm ot(inPin, outPin, false);

ICACHE_RAM_ATTR void handleInterrupt() {
	ot.handleInterrupt();
}

class OpenthermComponent: public PollingComponent {
private:
  const char *TAG = "opentherm_component";
public:
  Switch *thermostatSwitch = new OpenthermSwitch();
  Sensor *external_temperature_sensor = new Sensor();
  Sensor *return_temperature_sensor = new Sensor();
  Sensor *boiler_temperature = new Sensor();
  Sensor *pressure_sensor = new Sensor();
  Sensor *modulation_sensor = new Sensor();
  Climate *hotWaterClimate = new OpenthermClimate();
  Climate *heatingWaterClimate = new OpenthermClimate();
  BinarySensor *flame = new OpenthermBinarySensor();
  
  // Set 3 sec. to give time to read all sensors (and not appear in HA as not available)
  OpenthermComponent(): PollingComponent(3000) {

  }

  void setup() override {
    // This will be called once to set up the component
    // think of it as the setup() call in Arduino
      ESP_LOGD("opentherm_component", "Setup");

      ot.begin(handleInterrupt);

      thermostatSwitch->add_on_state_callback([=](bool state) -> void {
        ESP_LOGD ("opentherm_component", "termostatSwitch_on_state_callback %d", state);    
      });
  }
  float getExternalTemperature() {
      unsigned long response = ot.sendRequest(ot.buildRequest(OpenThermRequestType::READ, OpenThermMessageID::Toutside, 0));
      return ot.isValidResponse(response) ? ot.getFloat(response) : -1;
  }

  float getReturnTemperature() {
      unsigned long response = ot.sendRequest(ot.buildRequest(OpenThermRequestType::READ, OpenThermMessageID::Tret, 0));
      return ot.isValidResponse(response) ? ot.getFloat(response) : -1;
  }
  
  float getHotWaterTemperature() {
      unsigned long response = ot.sendRequest(ot.buildRequest(OpenThermRequestType::READ, OpenThermMessageID::Tdhw, 0));
      return ot.isValidResponse(response) ? ot.getFloat(response) : -1;
  }

  bool setHotWaterTemperature(float temperature) {
	    unsigned int data = ot.temperatureToData(temperature);
      unsigned long request = ot.buildRequest(OpenThermRequestType::WRITE, OpenThermMessageID::TdhwSet, data);
      unsigned long response = ot.sendRequest(request);
      return ot.isValidResponse(response);
  }

  float getModulation() {
    unsigned long response = ot.sendRequest(ot.buildRequest(OpenThermRequestType::READ, OpenThermMessageID::RelModLevel, 0));
    return ot.isValidResponse(response) ? ot.getFloat(response) : -1;
  }

  float getPressure() {
    unsigned long response = ot.sendRequest(ot.buildRequest(OpenThermRequestType::READ, OpenThermMessageID::CHPressure, 0));
    return ot.isValidResponse(response) ? ot.getFloat(response) : -1;
  }

  void update() override {

    ESP_LOGD("opentherm_component", "update");
    
    bool enableCentralHeating = heatingWaterClimate->mode == ClimateMode::CLIMATE_MODE_HEAT;
    bool enableHotWater = hotWaterClimate->mode == ClimateMode::CLIMATE_MODE_HEAT;
    bool enableCooling = false; // this boiler is for heating only

    
    //Set/Get Boiler Status
    auto response = ot.setBoilerStatus(enableCentralHeating, enableHotWater, enableCooling);
    bool isFlameOn = ot.isFlameOn(response);
    bool isCentralHeatingActive = ot.isCentralHeatingActive(response);
    bool isHotWaterActive = ot.isHotWaterActive(response);

    // Set temperature depending on room thermostat
    if (thermostatSwitch->state) {
      ot.setBoilerTemperature(heatingWaterClimate->target_temperature);
      ESP_LOGD("opentherm_component", "setBoilerTemperature  at %f °C (from heating water climate)", heatingWaterClimate->target_temperature);
    }
    else {
      // If the room thermostat is off, set it to 10, so that the pump continues to operate
      ot.setBoilerTemperature(10.0);
      ESP_LOGD("opentherm_component", "setBoilerTemperature at %f °C (default low value)", 10.0);
    }

    // Set hot water temperature
    setHotWaterTemperature(hotWaterClimate->target_temperature);

    // Read sensor values
    float boilerTemperature = ot.getBoilerTemperature();
    float ext_temperature = getExternalTemperature();
    float return_temperature = getReturnTemperature();
    float hotWater_temperature = getHotWaterTemperature();
    float pressure = getPressure();
    float modulation = getModulation();

    // Publish sensor values
    flame->publish_state(isFlameOn); 
    external_temperature_sensor->publish_state(ext_temperature);
    return_temperature_sensor->publish_state(return_temperature);
    boiler_temperature->publish_state(boilerTemperature);
    pressure_sensor->publish_state(pressure);
    modulation_sensor->publish_state(modulation);

    // Publish status of thermostat that controls hot water
    hotWaterClimate->current_temperature = hotWater_temperature;
    hotWaterClimate->action = isHotWaterActive ? ClimateAction::CLIMATE_ACTION_HEATING : ClimateAction::CLIMATE_ACTION_OFF;
    hotWaterClimate->publish_state();
    
    // Publish status of thermostat that controls heating
    heatingWaterClimate->current_temperature = return_temperature;
    heatingWaterClimate->action = isCentralHeatingActive && isFlameOn ? ClimateAction::CLIMATE_ACTION_HEATING : ClimateAction::CLIMATE_ACTION_OFF;
    heatingWaterClimate->publish_state();

  }

};

opentherm_switch.h

#pragma once

#include "esphome.h"

class OpenthermSwitch : public Switch {
 public:
  void write_state(bool state) override {
    // This will be called every time the user requests a state change.

    ESP_LOGD("opentherm_switch", "write_state");

    // Acknowledge new state by publishing it
    publish_state(state);
  }
};

Hi rdehuyss,

Yes, my intention is to contribute to ESPHome with the integration of OpenTherm.

I have ideas of how to do it but I need to take time (currently I'm busy with other things).

It's a challenge for me to express myself in English and program in Python, my native languages are Spanish and C# ;-)

Anyway, I am looking forward to making this contribution, I hope to have some free time soon

P.D: In my house I have the heating working with this code. So, we could say that it is suitable for production ;-)

Happy to assist in any lingualities if needed. I am fairly fluent in English and Spanish (amongst others). When looking at your code, I see mostly comments in Spanish. Could take a pass at translating.