Viessmann vitodens 200 low modulation low run time high return temp

[Johntheo5]

Can or have you range rated the boiler output??, on Vaillants the output can be range rated in kw.

 

[monkeysballs]

I tried it didn't seem to do anything
But I can turn it down to min tomorrow it's done in% unlike the vaillant that was easy in kw

 

[Johntheo5]

The 100-w can be range rated doiwn to 20%, assuming yours is the same then this possibly means 32*20%, 6.4kw, be interesting to see the % modulation then.

 

[vulcancontinental]

Do you mean that the user can set a minimum and maximum fan speed? I'm asking because the OP seems to have a problem where the power never goes below 23% and I'm wondering if inadvertently the minimum fan speed has been set to 23%.

I don't know the Viessmann that intimately but on some boilers you can raise the minimum or lower the max but not the opposite. It should be in the manual.

 

[vulcancontinental]

Not on FB
All I can see is set Max output as a %

As far as I can tell when I see modulation 100% means no modulation I've seen it when using dhw some times
This is today's modulation history so 19 hours and the burn times
View attachment 298359

View attachment 298358

What does the Y axis represent on the burner on graph?

There seems a 9⁰C ∆T on F&R which o think is good on a low temp system.

I mentioned FB as there are groups of Viessmann installers on there very knowledgeable who have confronted these issues before and may be able to help.

 

[monkeysballs]

Y is status so on is 1 off is 0

 

[Johntheo5]

What does the Y axis represent on the burner on graph?

There seems a 9⁰C ∆T on F&R which o think is good on a low temp system.

I mentioned FB as there are groups of Viessmann installers on there very knowledgeable who have confronted these issues before and may be able to help.

The burner on periods are very low compared to the off periods, looks like the flowtemp shoots up to SP+trip hysteresis and then takes a long time to get the flowtemp down enough to refire the boiler so must be using a very low flowrate (if no anticycle).
Post #41 "There is no anti-cycle delay nor heating after hot water delay, it fires on demand." maybe there is one on CH?.

 

[vulcancontinental]

I might have remembered past post badly. There may be an anti-cycle delay but it is not adjustable as on other boilers.

The timeline is jolly annoying when trying to attribute a time to an occurrence, if I were a Viessmann installer I'd write and ask for a datum pointer at the three hourly period.

Interesting the return spikes when I've assumed a shower is run at 7 and 8 but the flow does not.

If I've read it correctly during the 15 hours or 900 minutes up till 3pm the boiler fired 35 times, the majority of the times at 23% modulation never once out of condensing mode.

I suppose the next step would be to start logging gas consumption regularly during the day to attribute actual usage and consumption to operation.

 

[monkeysballs]

I have 30 minute gas unless I sit by the meter

The return spikes I don't understand except I suppose it's heating at same time as dhw and it happens with it doing something as the sensors for those are on the flow and returns just under the boiler. It's in built flow temp is deep inside so isn't actually accurate as flow and return

 

[monkeysballs]

Oh I've set max output to 10% see what it does

 

[monkeysballs]

Max output at 10% has made no difference to modulation amount really and burn time is up slightly first one was 10 minutes the next was down to 8

 

[monkeysballs]

 

[vulcancontinental]

So it's been a bit better I'm now on a curve of .5 and +5

One thing I don't understand is why there is a dhw schedule on a combi? Also is there anything I can tweak to speed up the switch to dhw? It takes a bit too long for the Mrs to be happy

Just re-reading earlier posts. The control will be fitted to system or combi boilers, that's why there's a DHW schedule, we do the same.

Are there preheat options on that boiler? 24 hour, touch n go or smart preheat?

 

[Johntheo5]

View attachment 298390
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Max output at 10% has made no difference to modulation amount really and burn time is up slightly first one was 10 minutes the next was down to 8

10% output should be either 3.2kw or 2.7kw if the max CH output is 85% of HW output.
I would monitor the gas meter for that 1 minute, you should get between 0.004 and 0.005m3 consumption.
The final throw of the dice is maybe to reduce the modulation to 0% (if settable), this then should give that elusive minimum output of ~ 2.0kw?.

One display above shows Minimum Heating output 5, what does this mean?.

 

[monkeysballs]

I can't change 5 down only up so I imagine 5% is the fabled 1.8kwh even though 5% of 32 us 1.6