System boiler - OpenTherm

Usul

Hi - hoping to shed some light on the functionality between a System boiler and Tado. I've read some info here, on the Tado site - and also contacted support (..and still could have some details incorrect). Are we safe to assume that Combi boilers are able to connect to Tado through OpenTherm, and that System boilers communicate through a more more rudimental method using 'call for heat' (using a 'duel relay', I'm not quite clear on this, maybe the same thing?)?

I'm looking for an optimum setup to use with a new System boiler and megaflo (heating ~15 radiators and two showers) which I'm hoping this post will help me source. So OpenTherm appears to an obvs choice, if it was compatible. From contacting Tado support who now appear somewhat cold I was told "We only support Opentherm connections via Combi boilers. Normally in the typical UK heating systems we support only dual relay connections and tado° acts as a standard programmer." which all appears pretty clear language.

However as I understand System boiler manufactures have their own Smart Thermostats, and Tado is able to connect using the manufactures language. So are there certain System boilers which have more advanced features similar to Opentherm (or even using Opentherm?)? Or are System Boilers just limited to call-for-heat and I should just go out and buy an efficient one compatible with Tado?

Finally, is Opentherm just the ability to modulate heat efficiently? Or does it involve further some other Tado functionality, such as taking in weather.

Thanks for reading, and answering!

Usul

GrilledCheese2

Temperature modulation is achieved with bi-directional communication between thermostat and boiler. When both the thermostat and boiler know the current room temperature and the desired room temperature, they can work together to ensure the room temperature does not overshoot. Communication is done with a digital bus using Opentherm or the manufacturer’s proprietary standard. They mostly achieve the same result, just using different languages.

The big advantage of using the boiler manufacturer’s thermostat controls is the ability to control the flow water temperature. For example when the cylinder is calling for heat the boiler can run at a water temperature of 70°C to quickly heat the cylinder and ensure the water is heated above 60°C. But when only the radiators are calling for heat the boiler can run at a lower water temp of 55°C to ensure the boiler is always condensing and working at maximum efficiency.

If you search this forum I think you’ll find some people are using the digital interface with system boilers, giving them the temperature modulation that you desire. But what they probably lack is the ability for Tado to modify the flow water temperature on the fly.

rossyl

@GrilledCheese2 just been researching, found this, and it's given me the answer I needed...but was hoping not to hear.

Do you know if Tado can now control the Flow Water Temperature on a System Boiler?

Thanks.

GrilledCheese2

@rossyl Opentherm cannot work with an S or Y plan system boiler when using Tado. It used to be possible to use digital control with Vaillant system boilers using an additional device called a VR65, but that is no longer possible since it was replaced with the VR66. In the absence of digital control there won't be a method to control the flow temperature.

rossyl

@GrilledCheese2 Many thanks.

I'm intending to have a Domestic HW Priority System.

It does not seem that Tado can work with Vaillant or Viesmann's weather comp, and therefore it's unable to benefit from weather compensated temperature flow rates.

On that basis, I think I'm going to stick with the boiler manufacturers own controls.