How to choose radiator and boiler (OpenTherm) system for a house?

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Hello, I’m considering options of temperature control in the house where I have multiple radiators and a boiler which can set the temperature of the water in pipes. I am new at this topic so any silly mistakes are possible. I intend to be able to control each room separately but at the same time keep the boiler on only when it’s needed. Also, I don’t need to keep the temperature in the pipes always the same.

So, I bought a few Devolo TRV (valves) already. They have Z-wave and can feed HA back about the temperature, and they are cheap. I believe my way to go is to have more of them or other z-wave/zigbee based TRVs. Here’s everything mostly simple: if the temperature is less than desired - open the valve. If there’s a window open - shut all the valves. Switch it on if somebody in the room for a while. And so on. This task I would love to outsource to HA automations. I like the automation format. However, I’m would love to know just one thing. Can my TRVs be closed completely and opened completely from HA? I suppose even if there’s no direct command then I can set the temperature to minimal to close and maximum to open.

Next, I’m going to buy a smart thermostat which I would love to manage from the HA. It should be able to switch on and off the boiler and set the temperature to certain ranges. I don’t want to control it continuously like to set 45° here, and then 44° in a minute, etc… I think it’s easier to automate to set 75° to warm the house quickly once we get home, then keep 60°-65° during active hours, and set let’s say 45° during the night.

I see a few problems here. First of them is the thermostat itself. There are many options but none of them looks exactly as I desire. I’m not talking about “exterior”. I cannot figure out how exactly it should operate. I find Plugwise as a very promising option. However, due to lack of knowledge in HA, I don’t know would it be possible to achieve with that integration. Second, if this is a thermostat then it has its own temperature sensor and will try maintaining a temperature at the set level. Basically, I want the thermostat to be smart in terms of connectivity and dumb when it gets working as a separate unit.

I can let HA be the heart of this because I cannot see why anything else would be more reliable. All other options are either vendor locked or too expensive. I considered Tado, Honeywell Evohome, and other vendor-based solutions. Do I miss something?

Hi, I have the same difficulty finding a thermostat. It should be able to connect with HA via wifi or ethernet (read and set temperature). When heat is needed, the thermostat should use opentherm to get the heater going. My family will use HA to set the temperature per room via the programmable radiator knobs (zwave). When the server is not functioning the temperature setting should be manually controllable (emergency fallback).
Oh, and the thermostat shall not ‘call home’ to an external website. Data stays in the house.

Did you already find a suitable thermostat?

Best regards,


Hi Maarten,
It turns out that almost any thermostat can do that with one little exception: all the communications go via otgw. this piece of electronics is actually small thermostat on its own. fully passive but still a one. otgw can work in two modes.

first is just scrapping the communication messages between the boiler and the thermostat. from these messages you can find out what are the values of most of the HVAC parameters here like water temperature or heating set point. otgw software kindly parses the messages for you so don’t need to hassle with all these opentherm protocol stuff.

the second one is actually a gateway. in this mode you’re make two other fooled because the boiler and the thermostat think that nothing changes. however, otgw substitute the original messages from thermostat to the boiler with those you set in otgw monitor (app on windows).

then you have your HA. it works as otgw monitor. so you can say to otgw to work in override mode (substituting commands in the message exchange) from HA. I’m not sure does otgw switch to the monitor mode when a server is down but it would be really nice if it does. If you can figure out this question with positive result it would actually solve your problem in a way you want.

After a few days of testing, I put my otgw in always override mode setting up heating set point to the temperature I desire for each part of the day.

A few tips along the way.

You can switch off water heating if you set heating setpoint to 10°C.

You can disable the override mode by setting a heating setpoint to 0. So that your thermostat will control the boiler.

Hope it helps. If not I would be happy to answer your further questions.

Hi Georgy,

after some searching I opted for the following:

  • 9 radiator valves z-wave (Z-Wave Spirit Eurotronic)
  • thermostat Opentherm Anna 24V/OT PLUGWISE
    All bought at ROBBshop in the Netherlands.

I already had a Aeotec z-wave USB stick, which I coupled to a Raspberry Pi 4b board using a USB hub. (The hub is needed due to an error in the USB port of the Pi board.)

Note: the valves are not re-transmitting in the z-wave mesh. You need intermediate z-wave devices (like a Fibaro wall plug) for radiator valves located far from the Raspberry with Aeotic stick.

The Anna thermostat comes with two parts: a thermostat with screen for in the living room. This one is connected via the 2-wire cable to the interface part, which you place next to your opentherm-compatible heater. Easy to connect with one screw-driver.

Home Assistant can talk to the Anna interface and you can read and set the temperatures on all devices. If somehow Home Assistant is not working, I can still control all devices manually by pressing buttons.

Plugwise is the most privacy friendly thermostat I could find.

Thanks for the info.


Just FYI, right now, the Plugwise Anna is offically supported in HA and support for the Adam HA is in alpha testing.

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Before a winter season started, a little update on the topic. OTGW NodeMCU version seems to be working after the winter of testing. Most of the functions you will figure out how to set up, even if it can be clumsy or quirky (based on your boiler). There are some problems you will get with integrity to HA (like that having many state changes in HA but the real-life state isn’t changed) but in general, it’s pretty good.
As a solution, it can be to use HA addon otmonitor

Another project you might have to consider if you’re willing to have more control over your boiler is this arduino/esp based project:

I have no clue what are the strong and weak points of this project.