What is it?

An OpenTherm thermostat shield to control a boiler or HVAC with an ESP32-S2 or an ESP32-C3 mini microcontroller. With this board you can control your OpenTherm enabled boiler or HVAC over Wi-Fi or BlueTooth, or integrate your boiler or HVAC with home automation systems like Tasmota, OpenHAB, Domoticz or Home Assistant.

Why did you make it?

Building your own thermostat is fun! I wanted to safe money and reduce my CO2 footprint by lowering Central Heating temperatures and thus making a HR condensing boiler more efficient. Also I wanted to make it easy to integrate in Home Assistant.

What makes it special?

It comes with programs to test the connection with your boiler, a full functioning basic thermostat example and a Arduino library designed in OSI model layers.

Now the Advanced_Thermostat.ino in the Github example directory is a ready-to-go thermostat specially designed for Home Assistant with MQTT integration. Just set your credentials in the program, flash it to e.g. an ESP32-S2 mini, connect the wires of your existing thermostat to the shield and add a Home Assistant Automation to send the room temperature to the thermostat. The Thermostat (MQTT HVAC) Climate integration will 'automagically' appear, together with sensors for boiler setpoint temperature, router RSSI signal level, a flame ON / OFF sensor, and, if your boiler supports it, water pressure, a flow temperature, return temperature, relative modulation percentage and Domestic Hot Water sensor.

If you are satisfied with the thermostat function you can put it away somewhere, out of sight, as long as there is WiFi signal!

A Dallas temperature sensor is on board and connected to a GPIO, however the microcontroller produces too much heat for useful readings.

With the ESP32-S@ mini mounted, the unit measures only 2.6 x 2.0 x 3.4 cm (W x H x L)

Note: the ESP32-S2 mini Mircrocontroller is included as an extra option!