OpenTherm Thermostat

€ 30.00


Shipping from the EU.

Smart WiFi OpenTherm Thermostat

Smart WiFi OpenTherm Thermostat with remote control for a cheap price and without any monthly costs. It supports all OpenTherm compatible boilers, has Home Assistant integration. Assembled and firmware flashed.

OpenTherm Boiler Connection

Boilers Compatibility

OpenTherm Thermostat is compatible with all boiler those have OpenTherm protocol support.

Easy Assembly

Just connect the thermostat to a boiler using 2 wires and power via any micro USB power adapter.

Simple configuration

Use WiFi Manager to setup WiFi connection. Select the Bluetooth temperature sensor or solder wires for DS18B20 temperature sensor.

OpenTherm Protocol Compatibility

The thermostat is compatible with all OpenTherm Protocol versions from the earliest to the latest.

Web interface

OpenTherm thermostat has it's own web interface, which simplifies configuration and provides remote control from your smartphone or computer

Home Assistant integration

The Smart Thermostat has Home Assistant integration which gives you remote control via Home Assistant application. Home automation, heating schedule using scenarios. Usage graphs.

OpenTherm Thermostat Connection

The thermostat connection is made as simple as possible. Just use 2 wires for the boiler connection and a micro USB charger as a power source.

WIFI OpenTherm Thermostat Connection

  • Optional. If you want to use built-in DS18B20 temperature sensor and wired connection you can solder it using wires up to 20m long.
  • Use two wires (up to 50m long) to connect the thermostat to an OpenTherm compatible boiler
  • Connect any micro USB charger as a power source for OT Thermostat.

Smart Thermostat Interface

WIFI OpenTherm Thermostat Interface


  • Thermostat Web interface. Access using web browser by the thermostat IP address:
  • Home Assistant application. Web access for desktop or native mobile application for iOS or Android.
  • Custom interface implementation using MQTT protocol

For configuration manual please refer to the Initial thermostat configuration page

In order to use thermostat you will need to configure at least WiFi connectivity first
Component Pieces
ESP8266/ESP32 Thermostat Shield 1
WeMos D1 Mini ESP32 1
Xiaomi Mijia Bluetooth Thermometer 2 LYWSD03MMC 1
Temperature sensor DS18B20 1
Micro USB changer, thermostat-boiler wires are not included.
Shipping method Estimated Time Fees
12-15 days €5.5
In order to use the thermostat you will need to configure at least WiFi connectivity first.
For configuration manual please refer to the Initial thermostat configuration page.
Stock firmware is not open source, but you can write your own firmware adding new cool features that fits your needs the best. DIYLESS Thermostat is based on Espressif's ESP32 Soc, which enables BLE/WiFi connectivity and allows writing a firmware using Arduino IDE, VS Code or IDF (Eclipse) IDE.
Also you can use ready-made firmwares like ESPHome, Tasmota etc.

If the stock firmware fits almost all your needs and only a few feature(s) are missing - we can consider adding them to the next version, please report a request or an issue report into our thermostat repo. Subsequent updates are free, and if you experiment on your thermostat with a custom firmware and later decide to rollback to the original one - we have a simple browser-based tool which allows you reverting back to the stock easily.
We use a PI algorithm which calculates the needed boiler power level based on a difference between current and target room temperature and also takes into account the speed at which this temperature rises/drops. It is aimed for the best comfort, meaning less temperature fluctuations.
That means the boiler will spend more in active state however at a lower power level instead of cycling between max power and off.
No, with a current control algorithm implementation you would not need a knowledge on outside temperature, because thermostat senses an internal temperature and once it drops - boiler will rise radiators temp to compensate.
In practice (from a real installation) - room temperature accuracy is held within a ±0.15°C range.
Yes, it does. However to use it properly - you will need to distance it from a board using a wires, since ESP32 self-heats a lot and sensor is heated by the board.
Out of the box it is controllable within your home network. If you need world-wide controlling options - one of the possible ways to achieve this is a Home Assistant with its companion app.