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ESP32 Opentherm Gateway

https://www.home-master.eu/web/image/product.template/59/image_1920?unique=7191457

The Opentherm Gateway is DIN-rail mountable OpenTherm gateway module designed to connect OpenTherm-compatible boilers with Home Assistant via ESPHome. Built around the ESP32-WROOM-32U microcontroller, it enables wireless integration of heating systems into modern smart homes, providing real-time control, automation, and diagnostics over Wi-Fi.

Ideal for intelligent climate control, the module supports full OpenTherm communication while offering local switching capability through a high-voltage relay output—useful for backup heat sources or zone control. Two independent 1-Wire buses allow the connection of digital temperature sensors, enhancing room-level temperature awareness and system feedback for advanced automation.

The Opentherm Gateway supports monitoring of burner status, flame level, setpoint temperature, system pressure, and water temperatures—all exposed to Home Assistant through ESPHome. It also includes a relay output for direct switching of heaters or valves, and dual 1-Wire interfaces for connecting temperature sensors such as DS18B20.

Powered by either 24 VDC or 220 VAC, the module offers reliable operation with LED indicators, USB Type-C configuration port, and OTA firmware update support. As with all HomeMaster modules, the firmware and hardware are open source, enabling easy customization and integration into advanced smart home systems.

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Firmware:

opentherm.yaml

Schematics:

MCUBoard.pdf

RelayBoard.pdf

Links:

GitHub


$ 120.00 $ 120.00 (Tax excluded)

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Display Name: ESP32 Opentherm Gateway

Function

It acts as a bridge between your heating system and Home Assistant, allowing real-time monitoring and adjustment of parameters like target temperature, boiler status, flame modulation, and more. The setup is compact, Wi-Fi-enabled, and leverages the ESPHome platform for easy configuration, OTA updates, and seamless integration into your smart home ecosystem.

Key Features

  • Controller
    ESP32-Wroom-32U
  • Designed special for ESPHome.
    All elements of the Gateway are fully compatible with ESPHome, ensuring optimal integration.
  • Input Voltage
    24V DC or 120VDC - 370VDC, 85VAC - 265VAC/47 - 63Hz
  • Built-in USB Interface
    For programming and debugging
  • Build-in Relay
    For supplementary equipment management
  • 2x1-Wire
    For extra temperature measurement

Gateway Capabilities:


  • Opentherm
    An Opentherm bus interface for managing heating equipment that supports the Opentherm protocol.
  • 1-WIRE
    Two channels designed for 1-Wire bus communication, featuring ESD and overvoltage protection to improve reliability.
  • Relay
    One high-performance industrial relay for control applications, equipped with varistor protection for enhanced reliability. The relay are optically isolated from the MCU.


  • LEDs and Buttons
    Customizable button positioned on the front panel, along with LED indicators for displaying status on the front panel.
  • WiFi and BT
    Integrated into the ESP32's WiFi capabilities
  • USB
    USB Type-C port for programming purposes.

Electrical Data


  • Power supply
    24VDC, 120VDC - 370VDC, 85VAC - 265VAC/47 - 63Hz,USB-C female (5V DC via USB-C) for programming
  • Power consumption
    typ. 1.2W, max. 2W
  • ESP32
    ESP32-WROOM-32U
  • 1-WIRE
    2-separate 1-WIRE bus, 5VDC bus power supply, ESD Protected
  • USB
    USBUSB type-C USB Specification 2.0 compliant, ESD protected, Silicon Labs CP2102N USB-to-UART bridge controller, Virtual COM Port Device Drivers, Works with existing COM port Applications, Supported on Windows, Mac, and Linux
  • Ambient
    Temperature 0 ... 50°C / 32 ... 122°F, Humidity max. 95% r.H. (non condensing)


  • Wi-Fi
    Reliablity HTOL/HTSL/uHAST/TCT/ESD,  Protocols 802.11 b/g/n (802.11n up to 150 Mbps), A-MPDU and A-MSDU aggregation and 0.4 µs guard interval support, Frequency range 2.4 GHz ~ 2.5 GHz
  • Bluetooth
    Protocols Bluetooth v4.2 BR/EDR and BLE specification, Radio NZIF receiver with –97 dBm sensitivity, Class-1, class-2 and class-3 transmitter, AFH
  • Digital Output
    1 digital output (relay with optocoupler and varistor surge protection), dry contact, 250VAC 16A at cosᵠ =1,250VAC 9A at cosᵠ =0.4, 30VDC 10A
  • OpenTherm
    7-15V DC with up to 35mA current