Viessmann WC setup questions

[dodgem101]

I recently (January) installed a Vitodens 200W with a sub-mounted mixer kit into my home as part of a refurbishment project. I have installed the WC controller and use the unmixed supply for the upstairs radiators, and the mixed supply for UFH downstairs.

So far I'm very happy with it, but I'm trying to get it setup to match my house a little better. In the cold weather, the temperature stays pretty much where we want it, so i think that the slopes, zero points, and set temps are ok:

Rads:
slope = 1.6, level = -1K, RTset = 20C
UFH:
slope = 0.9, level = -2K, RTset = 19C

Max flow temps are set to 74C for rads and 47C for ufh.

The problem is that with the warmer weather, and particularly when the sun is shining on the back of the house, it gets too hot, and the heating is still on (albeit at a cool temperature) when it's say 18C outside.

Should I be using the Summer Eco Function (coding address A5) to deal with this? And also the extended function (A6)? And how would I go about figuring out the appropriate time constant (address 90) for my house?

Or.... are these settings generally left as factory defaults and I actually have the basics of slope and level wrong for my house?

Any help from someone who is familiar with setting up Viessmann WC would be most welcome

Thanks!

 

[mysteryman]

Just select DHW only in the summer.

 

[ALEC1]

by default the heating shuts down at 1c above set room temperature, you may find the the house has no requirement for heat at set room temp less say 3c...

there are parameters to alter this...

 

[dodgem101]

@mysteryman - When i decided to get a WC system for my heating, one of the factors i liked was that it seemed that once setup correctly, there would be no need to touch it. Selecting DHW only in the summer seems like a very crude way to reduce the heat in the summer, and indeed if (god forbid) we had a cool day in the summer, then the house could be too cold. I don't want to have to go and change settings on my heating controller depending on whether it's a hot or cold day!

@ALEC1 - that's the address A5 that i mentioned, I just wasn't sure if this was something that is generally left as factory default. If that's the correct way to deal with it then great, i'll go ahead and have a fiddle with it

It seems there's quite a few factors to consider when setting up a WC system correctly - i can see why some installers shy away from them!!

Thanks for the answers.

 

[ALEC1]

In fairness viessmann (and other manufacturers) are not very good at sharing information...there are lots of installers who would be interested in this type of technology, but the market is set up for the dumbest installer so we all suffer...


if you set A5 at -3 and the set room temp is 21, the heating won't come on until its averaged at 18c out side...why viessmann have the constant time factor at 23.7 hours I don't know but it works satisfactorily and doesn't need fiddling with.

Matching heat load to heat requirement which is what this weather compensation does is involved, but it must save energy over just flicking a switch and let everything fire up to maximum, and in Germany your boiler would be on the end of network connection making it easier!

 

[mysteryman]

I hear what you are saying. You can overcome this by using the party function on a rare cool summer day. Setting DHW only in summer has the further advantage that pump overrun after a DHW run retains the residual heat in the DHW circuit, rather than putting it into the radiators. Otherwise, you can increase the offset between outdoor temperature and indoor temperature below which the pump does not run. Take care when doing this that you do not lose prost protection in winter night setback conditions.

Weather comp is well worth having and persevering with to get the best results.

 

[dodgem101]

Thanks both of you.

I take it that the second option you talk about mysteryman, is the same as the A5 setting that ALEC1 and I mentioned. I see your point about the frost protection. My night setback is 7C for the rads and 12C for the ufh, and I've now set the difference to -4K so even at night the rad circuit will come on at 3C and the ufh at 8C. I think there are seperate settings for frost protection that will override the set room temps anyway, but it's as well to be wary since a wrong code could indeed turn off frost protection!

I'll see how i get on with these settings now - the downside to WC is that it takes some time to see if it's working satisfactorily...

By the way, does the advantage of the pump overrun being kept on the DHW circuit still apply given that I have a combi boiler?

 

[mysteryman]

Yes. The DHW comfort - or pre-heat - facility is normally enabled at the same times as CH comfort. Pump overrun goes into the heating circuit when DHW & CH is selected, but stays inside the boiler with DHW only selected on a combi. You can time the pre-heat separately if you wish.