I just noticed that the central heating boiler in our flat supports the #opentherm protocol, and that there are controller devices for it which communicate with electronic radiator valves and temperature sensors to control not just on/off state but heating and tap water temperatures ... not cheap but might save us a lot of gas. but it's hard to finnd the options that make sense for us.
Does anyone know a site that has a decent overview, or experience with one of the "smart" openTherm setups?

Ok this been long overdue.
Sometime ago I've asked about #opentherm recommendations and promised that I'll get back with it.
So after all this searching, reading, finding (with very valuable input from @agaturcz@circumstances.run) I've decided to go with DIY solution from https://www.nodo-shop.nl/ I might add some external thermostat (as advised by author of the solution) later on.
I guess the most valuable thing that shifted my whole thinking was this piece https://seanblanchfield.com/2022/02/automating-heating-with-home-assistant found by @agaturcz@circumstances.run. After some fiddling I found out I don't need smart TRVs at all. I've spent a few days fiddling with dumb ones and barely touched them since then (a few bucks saved).
So thank you all that helped me here :)

@nameLess I must admit I am everything but expert about #OpenTherm. I've just started digging into it recently and I have only basic understanding. I have some impression, which I am going to share below, but please remember that I might be wrong. Please consider that as a good starting point for further research. If you find anything valuable I'd be glad to know. Especially if I am wrong.

So, we have following entities: gas boiler, thermostats (sensors+valves' actuators), central unit (ST-2801 or #TermetComfort), and #HomeAssistant. The central unit knows from programming what is the expected temperature in given room at the time, and from sensor what is current temperature there. According to the data it opens valve and turns on the boiler. The communication with the boiler goes either using on/off method (as you have called it: short circuit) or with OpenTherm protocol. The 2nd way allows to use the boiler more efficiently. You do not need to heat the water to 70°C if you just need to raise the temperature in one room by 0.5°C. Also, the central unit can read back some parameters from the boiler (required water temperature, water temperature on output, temperature of returning water, is DHW - domestic hot water - being provided at the moment and a few more, depending on the boiler).

The central unit - depending on the producer - may or may not allow to connect a temperature sensor by wire using OpenTherm protocol. However it is unknown to me, which device is superior. OT operates in a way, that one device initiates a communication and either ask the other device to perform something or polls for current state. In case of controller/central unit and gas boiler, the first one is controlling the communication with the other one. I have no idea how it works with OT-enabled sensor and central unit. So, there is a chance that you will be able to talk from HA to the central unit using OT integration, but I do not have enough knowledge to tell if that's possible.

As for HA integrations. Apart from officially supported ones, there is a service called #HACS (Home Assistant Community Store). It provides many add-ons, extensions and integrations. However, it seems the only way to find what is already supported there is to install HACS first, then browse it from HA level. So, there is a chance someone has written the Tech or #Termet integration and made it availabe through HACS.

@agturcz looks like we're after same thing (well mostly, probably 😉)
You're one step ahead because you already have #opentherm controller. Mind you sharing what is it? And how it interacts with #HomeAssistant ?
TIA

I just got new gas heating system for my home (replaced coal based). Now I was thinking about getting some #opentherm and connecting it to #homeassistant. What I don't know is what should I consider while choosing controller? I'd like to let #homeassistant control (at least to some point) the heating.
I was thinking about ST-2801 by Tech (it's a bit pricey) but maybe there are some other sollutions?
TIA

Anyway, if you have some recommendations I'd be glad to hear them.

My requirements are as follows.
Must have:
- temperature zone control
- working with #OpenTherm gas boiler
- integration with #HomeAssistant from class Local Polling or Local Push
- local access to the configuration, without the need to create an account in the cloud

Here is a blog entry about my brand new experiences with a #SmartHome application.

https://zb3.org/agturcz/broken-by-design

#TemperatureZoneControl #Plugwise #OpenTherm #Zigbee #HomeAssistant