Hey all! I’m Elvin, and I run a little website I call elvinhome. I’m one guy based in the Netherlands and I make the ESPHome-based devices that I want to see in the world. About half a year ago, I released the CTRL ONE, a smart thermostat & air quality monitor with a touchscreen ePaper display.
It was a great start, but it only supports a few types of heating systems. I’ve been working to expand that range, so I made the THRM ONE, an ESPHome device that connects to an OpenTherm-enabled boiler and exposes full control in Home Assistant.
A late prototype unit of the THRM ONE. Excuse the slightly burned water leak connector, I had to do some hand soldering!
You can find the full details on the product page, but here’s the rundown:
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100Mbit Ethernet. To give greater reliability than wireless communication, to boilers that are often stuck in the corner of the house with bad reception.
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ESP32-C6 for WiFi, Thread or Zigbee. If you do want wireless, you can configure the one that works for you.
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Water leak detection. The wired water leak sensor can be placed under the boiler to expand the diagnostics capability of the device further.
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Backup temperature sensor. A simple onboard NTC can be used if Home Assistant goes down, to keep things from freezing.
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Flexible mount options. The case has screw mounts, and magnets in the base so it can be placed on the metal casing of the boiler. You can also get it without the case, and 3D print your own.
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Wide range of power inputs. It can be powered over USB-C, or 5-28V DC through the screw terminals
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Opto-isolated OpenTherm interface. The terminals for the boiler are isolated from the rest of the board, so a bad power supply to the THRM ONE won’t damage your boiler.
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Made for ESPHome certified. You can find it here! elvinhome THRM ONE OpenTherm Master with Ethernet - ESPHome Devices
And I’ll be releasing the KiCad files under the CERN-OHL-S license once the first units go on sale, so you have the full schematics and PCB design files available. I’ve put a lot of work and many iterations into the design, but I built on the great open-source work of others before me. Just made sense for me to do the same.
While I’ve done extensive testing and I’m at the point where I can deem them safe and reliable, there’s another very important part on the equation: the boiler. I’ve got a simulated boiler I use for testing on the bench, and I’ve tested it on a real boiler, but I need more data.
I’ve got 4 THRM ONEs I’d like to give away for free, to those who are willing test it. I’m of course expecting you to report back with any issues and how it’s going, but if it works fine, I don’t want it back! These are final prototype units that have some very minor issues that don’t affect OpenTherm functionality (mostly just component placement, NTC temperatures a bit off, that kind of thing).
I’m centralising it on a Reddit thread so if you’re interested in getting a unit, leave a comment here: Reddit
You must live in the EU or the UK. Of course if you just have questions about it, I’m happy to answer them here.