Vaillant vSmart - Any experts out there?

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We have a modern, thermally efficient house. Last year we replaced our boiler with a Vaillant ecoTec model. Due to compatibility issues with our existing Honeywell room stat we had to replace that too, so we went for Vaillant's vSmart control system.

According to the Vaillant advertising (such as this video) the vSmart is supposed to modulate the heating flow temperature when the room stat reaches the setpoint. By running at a lower flow temperature the boiler is more efficient and its service life is theoretically extended because thermal shock is reduced.

However, our experience is quite different. The boiler runs at a very high flow temperature (70°C or above) and keeps running at that temperature even when the room stat has reached the setpoint. The boiler then switches off several minutes later and the heating overshoots by a good 0.8 - 1.0°C. It then doesn't come on for several hours while the house cools down.

This morning, for example, the temperature outside was 2.6°C, the vSmart was requesting a flow temperature of 83°C (D.009 eBus target temperature), and the boiler was maintaining a flow temperature of 75°C (set as a maximum in the boiler settings) with a heating return flow temperature of 65°C. Over the past two weeks, the highest D.009 temperature we've seen is 85°C and the lowest is 70°C. This seems very high. It also results in radiators that are almost too hot to touch and uneven heat distribution in the rooms.

The vSmart app shows the system using the "Advanced" algorithm, and it has set its own heating curve to just 0.7.

The screenshot below illustrates the fluctuations we're experiencing - nothing like the graph in the linked video.

It looks to us as though the vSmart isn't doing what it's supposed to do. Do you think the vSmart is faulty, or are there some settings (either on the vSmart app or the boiler itself) that we need to check?
 
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Not Vsmart, but an earlier Vaillant smart system the 407...

I have the boiler set for CH temperature at a max of around 55C, HW at 80C. I set the CH at 55C, to ensure it remains in the condensing range. The compensation setting at around 1.3.

It all works perfectly, with no overshoot and very economically. When there is a sudden call for heating, to increase the temperature from a cooler setting, it never outputs at more than 50C and does so very quietly, which suggests it is modulating the boiler right down.

So I would suggest checking the max setting in CH mode and reducing the compensation setting, either could cause it to over-react.
 
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That's interesting. I've read that the CH temperature on the boiler should be set to the maximum value so that the vSmart has the full range of temperatures to work with. My feeling is that the vSmart is requesting a higher CH flow temperature than it should. Of course, we could reduce the maximum CH temperature on the boiler, but we feel that the vSmart should be doing all that for us. That's why we bought it.
When you say "compensation setting", would that be the heating curve as shown in the vSmart app? If so, we've experimented with that previously, and changing the heating curve has made no difference to the CH flow temperature requested by the vSmart.
 
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When you say "compensation setting", would that be the heating curve as shown in the vSmart app? If so, we've experimented with that previously, and changing the heating curve has made no difference to the CH flow temperature requested by the vSmart.

Yes, that's what I meant. Vaillant don't have much to say about how it all works, but I think it decides what to do based on that setting, plus it seems to auto learn a little too.

Too be honest, I have never tried my system set with the full range of temperature for it to use. I had the new Vaillant boiler installed, originally using my old timer and stats. That meant it had to be set for just one output temperature, the higher one needed to satisfy the HW heating. The result was the boiler running flat out until the CH reported it was satisfied, with not much modulation and a lot of noise from pipes creaking as the heated and cooled, plus over-shoot in room temperatures.

So I bought all the Vaillant kit, including the outdoor sensor, spent ages tweaking it and now it works very well indeed. The boiler runs at minimum most of the time, the radiators are just barely warm instead of the hot and cold before and the room temperatures remain stable within a fraction of a degree. The boiler is in a kitchen cupboard and the only time I hear the boiler run, is when the HW cylinder is set to heat up.
 
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Thanks, Harry. Your heating's obviously doing what ours should be doing!
 
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Simply reducing your boiler output temperature should reduce the over shoot.
 
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I appreciate that. Our issue is that we've bought an expensive system that's designed to take care of that side of things, so we shouldn't be changing things manually.
If we reduce the maximum temperature on the boiler, I suspect the vSmart will still call for a much higher temperature via the eBus connection, and the fact that the boiler is restricted will probably have a negative impact on the vSmart heating algorithm.
 
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Which boiler do you have? Can you check setting d9 - this should show what temperature your vsmart is requesting:

d.09 Heating flow set target temperature that is set on the eBUS room thermostat
 
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Hi Fezster.

Our boiler's an ecoTec Plus 624 system boiler.

As I said in the original post, D.009 shows values from 70° to 85°C. They vary a bit, but they're always very high - probably too high for the boiler to be condensing. The eBus flow temperature doesn't change once the boiler's fired up, and doesn't modulate at all.

The maximum flow temperature on the boiler is set to 75°C, as recommended by Vaillant.
 
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The maximum flow temperature on the boiler is set to 75°C, as recommended by Vaillant.

I could not see any advice from Vaillant in my manual in regards to that. If your heating system is very capable of bringing your home to temperature in a reasonable time, why not limit it to a maximum temperature in the more economic condensing range?

Its 6.9C outdoors at the moment, my boiler is ticking over at around 36C, to maintain the house at a measured in the hall 18.5C.
 
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You're right, Harry, the manual is a bit vague on certain points. We actually got the advice from Vaillant (RochesterTechnical) directly:

"Both hot water and heating settings on the boiler should be set to maximum, as the vSMART is a weather compensator it will aotomaticallyl adjust the boiler target flow temperature depending on the outside temperature.

Regards

Dawn
Technical Assistant
VAILLANT"
 
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Dawn
Technical Assistant
VAILLANT"

The same Vaillant who were unable to answer me, when I asked if my system did or didn't set its own time date via MSF timecode, as it hinted at in the manual.

Why not as a test - see how it performs with a lower output setting for CH? You can always change it back..
 
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Thanks. We can certainly change the CH flow setting, which will reduce the flow temperature, cause the boiler to run more and improve efficiency. It may come to that in the end. However, we've invested in the vSmart, and we'd rather have it working properly.
 
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Sorry - I didnt read your original post properly, and missed the part about checking d.9.

You are right, though. The front panel control should be set on maximum and the vsmart should vary the flow temperature. Setting the front panel lower would work with or without an ebus controller - so defeats the purpose. You want the flow temperature to gradually be lowered as the system comes up to temperature.

I dont know enough about the vsmart, but does it have adjustable curves like other weather compensators? Maybe the delta to outside temperature is driving the high flow temps?
 
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Sorry - I didnt read your original post properly, and missed the part about checking d.9.

I dont know enough about the vsmart, but does it have adjustable curves like other weather compensators? Maybe the delta to outside temperature is driving the high flow temps?

No worries! The vSmart smartphone app is used to manage the vSmart's heating curve. It can be adjusted manually, or allowed to choose its own level. It then uses local weather data from the Internet to calculate the appropriate flow temperature for our house's characteristics.

The vSmart has chosen a value of 0.7, which is extremely low, and should therefore cause it to request very low CH flow temperatures. However, the requested temperature is never less than 70°C. We've experimented in the past with different heating curve values, but they've made no difference to the flow temperature being requested at D.009.
 
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