Viessmann Weather Compensation

[Johntheo5]

. During the day the room stat doesn't do anything as it's set above the highest temp that the room gets to (20 deg).

Do you mean its set lower?.

 

[tech749]

Do you mean its set lower?.

No, it's set to 23 during the day, the room temp hovers around 20-21, so doesn't activate. At night it's set to 18, so again didn't activate as room temp is higher than that. I'm talking about the controller, and not the boiler, that is set to 20.

 

[Johntheo5]

What exactly is the controller doing when its set to 23C, ie what is the controller output doing, is it a analogue output or digital, ie on/off.

This makes sense "At night it's set to 18, so again didn't activate as room temp is higher than that. I'm talking about the controller, and not the boiler, that is set to 20." but the day setting doesn't, it would, (to me) make sense if the room temp hovers around 23C and its setting was 21/22C?.

 

[tech749]

What exactly is the controller doing when its set to 23C, ie what is the controller output doing, is it a analogue output or digital, ie on/off.

This makes sense "At night it's set to 18, so again didn't activate as room temp is higher than that. I'm talking about the controller, and not the boiler, that is set to 20." but the day setting doesn't, it would, (to me) make sense if the room temp hovers around 23C and its setting was 21/22C?.

It's just digital, ON when room temp is below 23, and OFF (at night) when above 18. So WC has full control. ie. I'm letting the WC set the room temp for me (20/21). It rarely reaches the set point (23), unless cooking or something, then it will turn the boiler off until it drops below 23. I just move it to a cooler room then, so the other rooms don't get cold. I don't want the boiler to be switching on and off during the day, hence the high set point. Did that make sense? I don't mind the questions.

 

[Johntheo5]

It's just digital, ON when room temp is below 23, and OFF (at night) when above 18. So WC has full control. ie. I'm letting the WC set the room temp for me (20/21). It rarely reaches the set point (23), unless cooking or something, then it will turn the boiler off until it drops below 23. I just move it to a cooler room then, so the other rooms don't get cold. I don't want the boiler to be switching on and off during the day, hence the high set point. Did that make sense? I don't mind the questions.

It doesn,t really because you say "At night it's set to 18, so again didn't activate as room temp is higher than that." which makes perfect sense as the room temperature would need to fall to < 18C to start the boiler, acting like any roomstat, but if its set to 23C and the room temp (during the day) is only 21/22 then it will activate and keep the boiler running until the room temperature reaches 23C?. You can't have it both ways, if the measured value is higher than the SP then boiler OFF, if the measured value is lower than the SP then boiler ON, if you have it set to 23C during the day then the room temperature must be higher than 23C if you don't want the boiler to come on, but once the temperature falls below 23C then it will fire up the boiler? but you say the room temperature hovers around 21/22C and the boiler still stays OFF even though the SP is 23C?

 

[tech749]

but if its set to 23C and the room temp (during the day) is only 21/22 then it will activate and keep the boiler running until the room temperature reaches 23?

Well it would if the controller was in charge, but the WC is now controlling the boiler between those temperatures, as I said the controller's sole purpose is to switch the boiler on and off according to the temperature I have set for it. yes the boiler is running, but only to heat the house according to the heating curve, that's the general idea of WC is to keep the temperature steady. Boiler pump is on, but burner is modulating according to the flow temperature, sometimes burner is off, other time modulating at around 10%.

 

[Johntheo5]

Yes but if the house is hovering around 21/22C, which I assume you are happy with during the day, why do you want the boiler to be enabled/firing, it doesn't really matter what the WC is doing except that its setting the boiler target flow temperature so low that the actual boiler temperature is greater than that, in which case it will not fire, until the WC (say as the evening moves on) raises the boiler target temperature.
Why don't you set the controller to say 20C?.

 

[vulcancontinental]

Are there any trends out there showing the "room" temperature plotted against the OT temperature from people who are happy (apart from you?) with WC only control , NO roomstat.

What do you mean trends? I'm running my system configured WC, room stat sensor disabled so all the control app does is record room temp achieved by using the outside sensor only, no internal reference.

I can configure it so the comfort temp. achieved when timer contacts are closed then, when the boiler detects clock contacts open, it will recalculate a lower flow temp to maintain a setback setting.

The recalculated flow temperature is typically 8-12⁰C lower so the setback room temperature is 4⁰C cooler

The video shows the last 24 hours so the blue line is room temp, when I tap on the timeline at different points you can see fluctuations, afternoon when doors open and people in and out, late evening with doors closed watching TV. Hardly any fluctuation at all, less than a degree.

Midnight 22⁰C, doors closed, we stayed up watching TV then dropping to the regular temperature of 21⁰C.

If I used the two temps option the boiler would recalculate a flow temp overnight or when house empty between 8 and 12⁰C lower; approx 4⁰C cooler air than when on a comfort setting.

 

[tech749]

Yes but if the house is hovering around 21/22C, which I assume you are happy with during the day, why do you want the boiler to be enabled/firing, it doesn't really matter what the WC is doing except that its setting the boiler target flow temperature so low that the actual boiler temperature is greater than that, in which case it will not fire, until the WC (say as the evening moves on) raises the boiler target temperature.
Why don't you set the controller to say 20C?.

Sorry, not sure I understand, I may be explaining things wrong. The house is hovering around that because the WC is controlling it totally. I don't want the boiler to switch off and on around 20 C, that would sort of defeat the object of WC which is to maintain a steady temperature.

My understanding is that it does this by having the pump on at all times when boiler is set to on by the controller, and burner is controlling the flow temp accordingly (using WC). Otherwise the controller would switch off the boiler at 20 C, then depending on the differential would come back on when the temperature dipped, then go off again when it goes over 20 C. This would then cycle the boiler (I think thats the term), which from what I've read is to be avoided, plus the controller would be in control, resulting in from what I've read increase gas consumption as it has to restart the boiler again from a lower temperature.

I'm only using the controller to control when I want the heating on, which I can control remotely or for holidays etc. and at what temperature I prefer at night. Hope that clarifies, am I explaining it correctly?

 

[JohnOfChelmsford]

Read thread with interest as I've just had a Viessmann 050-w 30KW combi installed. I'm considering WC and as i understand it from the supplied manual, you can have an on/off stat connected too (not opentherm). So as @tech749 describes, this external hookup can be used to override what WC is trying to achieve by switching CH on or off based on a limiting indoor temperature.

I was wondering - do you need on/off stat because this boiler has only 'Standard WC" controls?

Reading this WC PDF from Viessmann, it seems to suggest Night Set-back is only available with 'Advanced WC' Can anyone with an 050 confirm. I've not been able to find a thread or video of anyone showing WC options on this boiler. If it isn't available, i can understand why you're using the on/off stat, and just considering if i'd do same. ta

<from manual>

 

[tech749]

Read thread with interest as I've just had a Viessmann 050-w 30KW combi installed. I'm considering WC and as i understand it from the supplied manual, you can have an on/off stat connected too (not opentherm). So as @tech749 describes, this external hookup can be used to override what WC is trying to achieve by switching CH on or off based on a limiting indoor temperature.

I was wondering - do you need on/off stat because this boiler has only 'Standard WC" controls?

Reading this WC PDF from Viessmann, it seems to suggest Night Set-back is only available with 'Advanced WC' Can anyone with an 050 confirm. I've not been able to find a thread or video of anyone showing WC options on this boiler. If it isn't available, i can understand why you're using the on/off stat, and just considering if i'd do same. ta

<from manual>
View attachment 329571

Hi John
I think the PDF you are looking at is a bit out of date, I was a bit confused by this document after mine was installed. The 050 range does have a limited Advanced WC, in that you can now adjust the curve as shown in the lower diagram by using the Vicare app, instead of being a fixed curve, which makes it a lot more efficient in my view. The things that aren't included are the ' Further Benefits ' as listed at the bottom of that page.

I use the controller to basically switch it off remotely by adjusting the temperatures day and night to suit my requirement. I was told that it is best to have the heating on at all times in the winter totally controlled by the WC, and it seems to work very well for me. In the latest cold spell the overnight heating did come on at about 0400hrs because the temp in that room dipped below 18 deg, it then regulated at that temp using the controller. We found that too warm in the bedrooms because they are warmer, so reduced it to 17 deg. I didn't want to go too low, as with WC it would take a while for the downstairs to reach room temp again, there isn't a boost function unless you want to ramp up the boiler set temp each time. But at 17 deg it doesn't come on overnight. I did reprogram it to come on 1 hour earlier to give it chance to heat up before we got up in case its lower than 18 deg. All working great now. Got my heating on all the time (both retirees) and still using less than my old system which was only on a total of 8 hrs, so really happy. Just had new loft insulation too which really helped keeping the house warm.

To answer your question I don't think there's a timer/temp set function on my boiler as far as I'm aware, which is why I wanted the wifi controller, which I can also use when we go away etc. Feel free to ask me any questions, I have a good understanding of the system now, I don't mind. Viessmann customer service email are also pretty good, usually get reply almost straight away. Hope this helped anyway.

 

[JohnOfChelmsford]

Hi - yep, i think you've confirmed that there's no set-back function with this boiler's implementation of WC and what you've done with the controller is clever. It does seem bizarre to me that this isn't available. I'll consider WC now as i can set up the same 'dead switch' style arrangement with my nest wired in on/off mode. It may even be best option for me as our boiler is below our bedroom and our house is old with solid walls, so would definitely fire many times during the night if left to WC control, which may be too noisy for a light sleeper like me

 

[tech749]

Hi, just put a thermometer in the room you normally use, and see what the temp gets down to on cold nights and set accordingly, or just set to come on earlier than normal as I did. Can always turn bedroom radiator off or set the rad thermostat lower when you go to bed, so it doesn't get too warm while you are sleeping if boiler comes on. The boiler is really quiet anyway, I can barely hear it when I'm stood next to it.