Vaillant VSmart: heating curve issue?

16 Nov 2022
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My Vaillant Ecotec plus VMW 35 has this heating curve. (A is outside temperature and B is the hating flow temperature)
Screenshot 2023-11-05 203545.png

I'm using it with VSmart remote control. I don't use advanced algorithm but the hysteresis one.

This morning outside temperature was 16°C in according with the app. I've my room setpoint on Vsmart at 20°C and my curve is 0.6
But the flow temperature for the heating was 50°.
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Even curve 4 at a OT of 16C is only asking for ~ 46C. (its just about possible that it is looking at this curve and that your boiler is very near cycling as it will if the flow temperature is/has reached Targettemp+5C)
Can you check D.009 & D.005.

You are the last poster below so assume you've read the posts.

Vaillant vSmart - Any experts out there?​

Last edited:
D.009 is 50: it's the desidered flow temperature; instead D.005 value increases to get D.009 value

I've read full "Vaillant vSmart - Any experts out there?" topic , but no replies answer to my question
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Hi, I have just given up on vSmart after 6 years of fiddling with the system every winter trying to get it to behave sensibly. I had begun to wonder if the heat curve setting is somehow doubled inside the black box, as I could never understand the flow temps the controller was requesting from the boiler - in the week that I replaced vSmart the daytime temps were about 10C and with a set point of 18.5C and a room temp of 18C the system was regularly requesting 75C from the boiler, which heated up the house quickly but caused big overshoots. This was with the advanced algorithm with heat curve 1.6, which I'd allowed the system to self select. I too have previously had the system set on hysteresis - with that setting I have found that the weather comp flow temps are more sensible, but the system then seems to not use load compensation, so if your room is 3-4C, or more, below set point it can take hours to get to temp.

I have now replaced vSmart with Sensocomfort wireless, and the flow temps requested from the boiler are much more sensible and correlate with the heat curve graph - I can only conclude that there's some serious errors in the algorithm and/or coding in the vSmart system that means it requests crazy temps.

If your vSmart is still in warranty it may be worth trying to get Vaillant to allow you to reject it on the basis that it's clearly not working correctly, and swap it to a SensoRoom controller with Myvaillant Connect box - this controller appears to do the same as vSmart (app control, internet weather compensation), but as it looks to have been developed by vaillant in house, I'd hope that it works much better. vSmart is essentially a Netatmo controller onto which weather compensation has been bolted, and that seems to be where the problem with it lie.

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