Nest V3 not modulating below 40C

[Martijn___]

My nest Learning V3 EU in my living room is set as OpenTherm. On my boiler I have set a max water temperature of 45C. The system is now modulating between 40 and 45C.  SP water temperature on boiler never comes below 40C. As I have floor heating and a very well in insulated house, I would like that the system modulates to 30-35C. Lower temperatures makes the boiler more efficient.

Why is my nest not modulating below 40C?

[Sonos]

First thing to check is the (voorloop) temperature in the nest settings.  That should be the same as the exit water temperature setting on your burner.  

But it might also be a setting in the heater (ketel). Some things to look for In most systems;

you can set the delta temperature modulation point. I.e. the difference between the exit (heated) and return water.  
you could check if it actually set to open term. (With an external controller)

the 0-10v setting could be set on capacity and on exit temperature. 

your system requires a minimum temperature drop before it starts and therefor will not keep it stable if you only loose a limited temperature in water.  I.e. it keeps pumping but not heating until it starts again full power. 

And last. How do you know it is not modulating? It might just keep the temperature stable so it only looks like the exit water is alway hot bu just uses a very limited amount of gas. In that case. Just set your exit water temp to 35c

[Martijn___]

The voorloop temperature setting on nest and max temp on Intergas heater are both 45C.

I have checked all setting in heater, they looks ok. Min power of heater is set 25%, so th

The display in heater shows SP water temperature that it gets from Nest. First it is 45, after a while it moves by 44-43-42-41 to 40. That's it .

I have checked all setting in the heater, they looks ok. Minimal power of heater is set 25%, so the heater can adjust to lower delta T. At the end heater goes to start-stop, but I think that will be always the case when a house with modulating system has reached SP temperature.

Yes, I can set nest to on/off mode fixed on 35C, but than I miss a faster start for the first hour with 45C water. And I just want to understand why it not goes below 40C.

[Vladut]

Hi there, just checking in with you. Did you manage to check the above message?

[Martijn___]

Without having changed anything, after 4 weeks I have seen temperatures below 40C as setpoint on my heater! Don't know why,  but it is working.

Does it takes  >4 weeks to learn? 

Will trueRadiant also correct overshoot? When in afternoon setpoint in the living changes from 17 to 20C I see everyday an overschoot to 21.

[AlexD]

It is great to hear it is working as expected now. It is possible though generally the water temperature is set from the display or boiler. 

True Radiant may be able to help. You can enable it and see how it behaves for a time to see how it behaves. Here is a link with more information on how it works and what effect it has on different systems. 

[george_t]

Hi @Martijn___. Just checking in, how's it going with your thermostat?

[AlexD]

Hey there, I haven't heard from you in a while so I'll be locking this thread. If you have any new issues, updates or just a discussion topic, feel free to start a new thread in the community. Thanks, AlexD.

[DragosC]

Hi there @Martijn___

Thanks for letting us know and thanks for reaching out. With the OpenTherm feature, the minimum you can set the hot water temperature is 40C. You can find more details in the following article: Domestic hot water control

"Tip: The minimum temperature setting for combi boilers with OpenTherm control (40ºC) (104ºF) is lower than hot water tanks (55ºC) (131ºF). Combi boilers do not store hot water in a tank and the risk of the formation of Legionella bacteria is very low."