Vaillant boiler - Flow temp?

[giorgosa]

Hi all,

moved to a terraced house recently, and changed an old Vokera boiler (15+ years) with a Vaillant 832 Ecotec Plus together with a Nest thermostat. Previous system was having only TRVs so probably highly inefficient. I am happy with both the boiler and the flexibility that Nest thermostat is giving me, given that we don't follow a specific schedule.

With the weather being cold, I was looking into boiler settings. The installer set the below:
D.000 to Auto
DHW tp 63C
CH to 75C

Rooms become warm very quickly(and radiators very hot as temp is 75C), and radiators turn cold for 2-3 hours when thermostat will make the system work again.

Are the above the most efficient for this boiler? Flow return temperature (from D.041) seems to be 66C, 9C less than CH setting, but shouldn't it be 55C for maximum efficiency?

 

[giorgosa]

Any ideas?

Temporarily I reduced CHW temp to 63C so that return flow is 55C-56C. It may take longer -very slightly- to heat but I believe that it is more efficient.

 

[Steelmasons]

Efficiency over comfort???..
Ask the installer to increase CO2%... That way you can have yer cake and eat it too..

 

[Agile]

Generally the boiler will be a little more efficient with a return temperature of about 55 C.

But your comfort should be the primary requirement.

I am guessing that it is a modern terraced house with good insulation and a very low heat loss so that it only loses as degree or two in a couple of hours once up to temperature.

However, as far as I am aware, if the Nest is the latest Mk III then it is able to control a boiler flow temperature automatically according to the amount of heat likely to be needed as based on outside weather temperature obtained from the internet.

But to do that in your case, it would need a Vaillant controller to interface the Nest which is not officially sold in the UK. Or instead a proper Vaillant weather compensated controller.

So my conclusion is that the Nest is only connected as an on/off controller which is less efficient than the proper weather compensation. But that seems to be what you have !

So it would appear that either the installer did not know what was possible, did not bother to tell you or perhaps you decided what you wanted and he just kept quiet and fitted exactly what you had asked him to!

The hot water setting is better at about 60 C.

Tony

 

[giorgosa]

Thanks both,

I didn't choose the nest thermostat, it was in the offers I received from several installers, it was seeming to have certain benefits (it has indeed) but at the time I didn't know the difference between a real Weather compnsator and the nest. It is a 3rd generation nest. Do we know why the controller is not available in the U.K.?

I need to try for some days the lower flow temp and see if we are comfortable. In general it seems that home keeps heating quite well; last evening it reached 20.5C at 19:30 and didn't again switch on till 22.30 when it was scheduled to turn off (with outside temp at 6C).

 

[Agile]

I would almost say that you were gently conned into buying a system which does not really give you the best that is available.

I am not an expert on the Vaillant controls which are pretty expensive generally.

It seems to be a commercial decision that as they have their own WC controller they don't make it easy/possible to use other makes with their boilers.

As far as I know they don't yet have a smart controller with Internet access like the Nest.

WC is a very good system and can offer savings in consumption of around 6%.

Internet control is to me a bit of a gimick. For a single person working irregular hours it could be useful. For anyone else somewhat limited in my view.

You could have Vailant WC with your boiler and still use the Nest as an internet on/off controller. Expensive option though!

Tony

 

[giorgosa]

I am really happy with the Nest thermostat as we don't follow a specific schedule, so auto-away and remote switch on are really really useful and energy saving I think.
Would I like to add more optimization (e.g. auto flow temp control etc)? Definitely yes, but if the system is restricting me then I need to manually find the optimal settings to fully utilize a highly efficient new boiler.
As I said, I'll try for a couple of days flow temp at 63C and see how we go with comfort. Given that return temp is 55C, this should be the optimal.

Do we know what economy we achieve with flow return temperature of 55C instead of 63C-65C? I wouldn't be surprised if the difference is low...

 

[Agile]

Could be a few %.

My guess would be about 5% better, perhaps!