Viessmann Vitotronics 200W Room temperature & Heating Curve

[D_Hailsham]

Still trying to figure out why the radiators were not heating up on the scheduled program time.
I've adjusted the programs for the DHW to start and finish 6am - 840am and the CH to start 06:40am - 9am.
I am assuming that 40 mins should be enough for the cylinder to be warmed up as this is given priority I was told.

Provided the boiler doesn't wake you up, why not bring it on earlier? There is then less chance of it clashing with the CH.

We had been finding at 20c the radiators were not getting warm for at least 45 mins or so and even then they were only slightly warm.
So room temp was increased to 25c now I am gradually bring temp down 2c a day.

Will try curve at 2 once temp testing had been completed.

Temp testing is a waste of time as the "thermostat" is not measuring the room temperature, it's just shifting the curve up and down, parallel to the standard curve, i.e the slope stays the same. As I said previously, leave the "stat" at 20 and change the curve to 2. If the house still doesn't reach 20, increase the curve and vice versa.

 

[puthsardarade]

Still trying to figure out why the radiators were not heating up on the scheduled program time.
I've adjusted the programs for the DHW to start and finish 6am - 840am and the CH to start 06:40am - 9am.
I am assuming that 40 mins should be enough for the cylinder to be warmed up as this is given priority I was told.

Provided the boiler doesn't wake you up, why not bring it on earlier? There is then less chance of it clashing with the CH.

We had been finding at 20c the radiators were not getting warm for at least 45 mins or so and even then they were only slightly warm.
So room temp was increased to 25c now I am gradually bring temp down 2c a day.

Will try curve at 2 once temp testing had been completed.

Temp testing is a waste of time as the "thermostat" is not measuring the room temperature, it's just shifting the curve up and down, parallel to the standard curve, i.e the slope stays the same. As I said previously, leave the "stat" at 20 and change the curve to 2. If the house still doesn't reach 20, increase the curve and vice versa.

So how long does the DHW needs to be on before it is satisfied and the boiler moves to the heating?
Does it make a difference if the DHW program ends before the heating program starts?

We need hot water from around 7am to 9am and heating at a similar time in the morning - what would you advise as the morning programming times?

I will try your suggestion about leaving it at 20c and then starting the curve at 2 etc.

Thanks

 

[Jackrae]

Only you know how long it takes
It is my understanding that DHW takes priority even if its programme is "OFF"
You can verify this by looking at the boiler output temperature - if DHW is in demand the boiler will be running around 70C, if DHW is satisfied the boiler will be running cooler (depends on curve)

 

[Jackrae]

double posted

 

[D_Hailsham]

Can you confirm that you have a Vitodens 200W boiler and a Vitotronic 200 HO1B controller?

 

[Jackrae]

Mine is a 200WB2C with H01B
One of the disadvantages it has is there appears to be no "easy" way of hooking up a room thermostat into the system : perhaps you can hopefully advise me otherwise.

 

[D_Hailsham]

My question was actually directed at the OP who said he had a "Vitotronic 200 W", which seems to be a mash-up of the boiler model (vitodens 200W) and the controller model (Vitotronic 200 W) which is used with heat pumps.

The clever Germans say you don't need to measure the actual room temperature - except when tuning the system. Provided the heating curve has been correctly adjusted, the house will maintain the required temperature, irrespective of the outside temperature (except when it's hotter outside).

 

[Anesta]

Thank you so much Hailsham, finally I have found somebody who can explain things in a very plain manner! I have just had a Vitodens 200 with the HO2B WC installed and I have written to the Viessmann Technical department with some questions, but I got the impression that noboby was actually reading the questions I was asking and that they were just giving me sentences out of a book!

Now I have understood that, when I set my room temp. as, say 18, there is NOTHING in the house that tells the boiler that I have reached my target temperature: it’s only based on the heating curve and the boiler knows that, if outside temp. is 5 in order for me to have 18 inside the water in the radiators should be X. In an ideal world.

So, am I right in thinking that the box I have in the house (looks like a thermostat) is only a tool that allows me to operate the boiler remotely? If so, it doesn’t really have to be fitted in the coldest spot of the house, like a conventional thermostat.

Is there any feedback at all from the house to the boiler? For ex., if I was to set target T at 18 but for some reasons (I have a party of 20 people, with all the lights on and the fireplace going as well) the temp in the house gets to 25 and outside T is -5, would the boiler still fire up?

Could you please help me with a questions which is still bothering me? Is it more economical/efficient having a smaller or a higher slope? Is it best to have a less steep slope with a higher desired T or a steeper slope with a slightly lower desired T?

And how about the level? How does that come into play?

By the way: system is great, there aren’t cold pockets in the house, the temperature in the house feels very homogeneous and pleasant. Even in periods of OFF it is not freezing (mind you, I have set it at 12: too high? Is it better to let the house go really cold during the night or keep it just cool?).

Hope you will have the time to reply!

 

[Jackrae]

Basically the slope of the curve determines what increase in heating is provided to the radiators for a corresponding decrease in outside temperature; for example say the water increases by 2 degrees for each 1 degree of drop in outside temperature, if you increase the slope then the water may now increase by 5 degrees for each 1 degree drop in outside temperature.

The slope required is determined by the material your house is built from. If it has high thermal transfer or loss type walls - say solid brick with no wall insulation - then you need a steep slope; if it has extremely well insulated walls then you need a flat slope since there is a low heat transfer or loss rate.

Therefore if your slope is set incorrectly (determined by experiment) your house will be either too warm or too cold for a change in outside temperature.

Because the "average" British house isn't built to conserve heat, finding the ideal boiler slope will be difficult and may end up as a simple compromise. In my case, I have a 100 year-old stone-built house with lath and plaster walls, I leave the slope at the 10k 1.4 default value and simply make a degree or 2 adjustment to the set-point as and when desired.

 

[Anesta]

Thank you for that, but what does it mean when you say that you leave the slope AT THE 10K?
Is it worth playing with the level?
Over the past two weeks I have used a range of combinations of slopes and set temperatures and I often achieve the same results with two particular slopes. But if I look at gas usage it varies a lot from day to day, irrespective of the slope (and I only compare days when the outside temp. is within 1-2 degrees ).
Is there a rule of thumb, like the lower the slope the lower the gas usage, or not?

 

[Jackrae]

Maybe you are confusing boiler efficiency with gas usage. Gas usage for a boiler (that is working correctly and efficiently) is directly related to the heat lost by the building interior to the external atmosphere. Theoretically it should matter not what temperature the boiler runs at providing it is running in its most efficient mode (ie condensing).

Altering the slope will merely affects the response time to changes in atmospheric temperature and whether or not the interior gets too hot or too cold.

The whole basis of the Viessmann control is that internal temperature can be maintained constant irrespective of the external ambient IF you have determined the 'curve' that best suits your property - and this can only really be determined by experimentation. Out of interest, is your external sensor mounted on a north wall as recommended by Viessmann. Also, does your rooms have radiator thermostatic valves as these will affect how the boiler operates - In the "ideal" Viessmann house build (so that probably excludes 99.9% of UK houses) thermostatic valves are not required so that all rooms lose heat to the exterior at a constant rate determined by inside-to-outside temperature differential and radiator output is determined by size and fixed balancing.

Variations in gas usage may be down to numerous factors, some atmospheric and some human. Can I suggest NOT changing the curve and monitoring usage over several days taking note of atmospheric conditions. Ideally you should take readings at say hourly intervals, of internal temperature, ambient temperature, whether or not the wind is blowing, from what direction and whether or not the sun is shining etc. That way you will see how usage can change dramatically due to variables over which you have no control.

 

[Anesta]

I'll do that. The sensor is mounted on a east facing wall. Wasn't there when it was done. The north wall is in a "corridor" that gets always windy, maybe that's the reason?

 

[Anesta]

Could I ask you what is the 10K you mention?
Is it worth moving the level? What does that do?