Nest 3rd Gen and Opentherm on S Plan system

[gingham-foliage]

Hi,

I'm interested in using a Nest 3rd gen with my Opentherm system boiler that is configured in an S plan setup. The wiring guide does not show this installation. Is it possible to do?

Thanks,

Theo

[DragosC]

Hi there @gingham-foliage. 

Thanks for reaching out. The thermostat has instructions for Combi OpenTherm only or system boiler with on/off. Could you tell us please if you've checked with the compatibility widget from our website? Here's the link for that: https://bit.ly/2ZOmnxX . 

[gingham-foliage]

Thanks for the link to the site. It says the system is compatible, but does not mention OpenTherm. Has anyone used Opentherm with a system boiler that is configured in S plan (or Y plan for that matter)?

[DragosC]

Great. The OpenTherm is not compatible with the S or Y plan. Those are on/off motorized valves. The OpenTherm modulation does not have valves for on/off. We're interested in the fact if the boiler was originally OpenTherm or is it a system boiler with an OpenTherm additional module installed after? 

[gingham-foliage]

It's for a boiler that has an additional module installed. My understanding is that these are usually configured so that the OpenTherm protocol is used to control the power (modulation) of the boiler, and the controller is still used to activate the appropriate valves. I've read on forums that Nest Heat Link will still activate the relays even when the Nest is in OpenTherm mode, allowing the valves to operate, and the boiler to module the power.

Are boilers with additional modules different from boilers with it fitted from the factory?

[DragosC]

Thanks for the explanation. In this case, it's not compatible with the OpenTherm part, just with the on/off settings system boiler. The Nest Thermostat is compatible just with the  Combi boiler OpenTherms that are like that from factory. You can learn more about what can the Nest Thermostats do with the OpenTherm combi boilers: https://bit.ly/3HeJohK

[AlexD]

Hi, I wanted to check in. Do you need any further assistance? If so, make sure to let me know. 

[gingham-foliage]

It would be great to know if the Nest Heat Link will still activate the relays even when the Nest is in OpenTherm mode

[DragosC]

The relays are activated by the On/Off function. The OpenTherm does not have anything to do with the relays. The OpenTherm keeps the system always on on different intensities.

[gingham-foliage]

Sorry, I'm so confused are you saying that the relays will continue to operate even when True Radiant is enabled - as they have nothing to do with one another. Or are you saying the opposite?

[DragosC]

I'm sorry for the confusion. The information is better explained here about the differences between the relayed heating and OpenTherm heating. Please take a look at it: https://bit.ly/3HeJohK

[AlexD]

Hi, I wanted to check in. Do you need any further assistance? If so, make sure to let me know.

[george_t]

It's been a while since this thread was last updated so I'll go ahead and lock this thread. If you're still experiencing problems, please feel free to start a new thread and we'll be happy to help.