How Does ZoneTherm Use W5500 to Connect Seven OpenTherm Heating Zones?

ZoneTherm combines seven OpenTherm thermostats, configurable valve groups and W5500 Ethernet for local zone control and Home Assistant integration.

Benjamin

Published September 07, 2026 · © MIT license (MIT)

166 UCC

11 WCC

31 VAR

2 Following

Original author: Max BrantsOriginal source (new tab)

Components

Hardware components

WIZnet - W5500

x 1

ZoneTherm PCB U3. ESP32-S3 uses ESP-IDF Ethernet over SPI2 at 20 MHz; CS GPIO10, IRQ GPIO14, SCK GPIO12, MOSI GPIO11, MISO GPIO13.

WIZnet parts

W5500 Datasheet

Project description

Seven Room Requests, One Shared Manifold ZoneTherm is an open-source controller design that connects seven OpenTherm wall thermostats to seven configurable valve outputs and Home Assistant. An ESP32-S3 handles thermostat messages and room decisions, an MCP23017 expander drives the valve bank, and a W5500 provides wired Ethernet for MQTT and the web interface. A room can control several valves when its floor-heating circuit contains multiple loops. Max Brants publishes the firmware, KiCad hardware and Svelte web UI under the MIT License. Valve-set control arrived in August 2026, with release…

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