Viessmann Vitodens 200-W B2HA heating issue

[kgfx_5]

Hello!

I have a large house, 20 radiators + UFH. Heated house area is about 350 m2. House is class B, it is written in the certificate that house requires 73 kWh(m2/year) for heating. I had my system fully upgraded last year, installed new Vitodens 200-W 49 kW (B2HA) model with Vitotronic 200 controls. I know I made a mistake when choosing boiler, I thought my model supports 1:17 modulation too, but unfortunately this is not the case with 49 KW version.

Last year I used it with Tado, but I didn't like Tado modulation, so I decided to give a try to Viessmann weather compensation this time. So, right now we have about +10 C outside, and my boiler short cycles unless I do 2 things - first I have to open all radiators and second, I have to insanely adjust heating curve, like we are talking about 1.3 slope and 12 level, so the temperature would be around 50 C when it is 10 C outside. When both this things are done, boiler starts, modulates and works for some time, after that some rooms with Tado TRV's are heated enough, radiators are closed now and boiler just stops, while half of the house is still cold.

After that boiler starts itself for 15 seconds each ~10 minutes, heats up to 55 C, turns the burner off and temperature (of course) drops immediately. Could it be that my boiler is simply too powerful for the system and cannot modulate low enough or there are other reasons for this behaviour?


Thank you all in advance.

 

[ShaunCorbs]

The problem sounds like it’s with the tado smart trvs try removing them all and see how things go if the house is too hot adjust the wc so the flow is less

 

[kgfx_5]

The problem sounds like it’s with the tado smart trvs try removing them all and see how things go if the house is too hot adjust the wc so the flow is less

Thanks. Do you mean just leave radiators all the way open?

 

[John.g]

(Why can't any first post be quoted in reply??)

"After that boiler starts itself for 15 seconds each ~10 minutes, heats up to 55 C, turns the burner off and temperature (of course) drops immediately. Could it be that my boiler is simply too powerful for the system and cannot modulate low enough or there are other reasons for this behaviour?"

THe TRVs are only doing what they are supposed to do, the flowrate reduces, the heat demand is less than the minimum boiler output and the boiler temp reaches SP+5C and burner trip followed by recycle, then on refiring it isn't able to modulate down from the ignition conditions before burner trip again at SP+5C. You don't say the boiler's minimum output?..
You need a relatively high flow rate, a ABV may help, and fairly long anti cycle time, the anti cycle time looks like its 10 minutes which should be ample time to get the boiler temperature down, it should certainly be long enough if you have a ABV.
In the meantime can only suggest yet higher temperature slope, or disable it and set the boiler flow temperature manually, if allowed.

 

[kgfx_5]

You don't say the boiler's minimum output?..

I think it can modulate to a minimum of about 11-12 kw. Regarding ABV - I have 2 towel holders that are always open + UFH collector with his own pump, so I guessed that flow rate shouldn’t be an issue?

 

[John.g]

That shocking 1:4.3 turndown to 11/12kw is the main problem IMO, also the boiler may fire up at ~ 25kw or more (ignition conditions) before modulating to 11/12kw, by which time the burner has shut down.
It may help to limit the boiler output (range rating), if menu available, see what its currently set to.

Also note the boiler flow temperature when it refires or while its in anticycle mode.

 

[kgfx_5]

That shocking 1:4.3 turndown to 11/12kw is the main problem IMO, also the boiler may fire up at ~ 25kw or more (ignition conditions) before modulating to 11/12kw, by which time the burner has shut down.
It may help to limit the boiler output (range rating), if menu available, see what its currently set to.

Yeah, I really made a mistake when I bought this thing thinking about 1:17 modulation. But I am also not sure that 32 kW would be enough for my home.
My plumber suggests to add a buffer tank into the system, could it help?

 

[John.g]

A buffer would definitely help IMO.

 

[gmartine]

Yes will require a LLH or at least CCT's. Can you provide a picture of the pipework surrounding boiler.

 

[kgfx_5]

Yes will require a LLH or at least CCT's. Can you provide a picture of the pipework surrounding boiler.

Sure.

 

[gpbeck]

73 kWh(m2/year)

Confused by the units here but if it's supposed to be 73 kWh/m2/year that is a total annual consumption of 25550 KWh. But what is the heat loss (in KW) at -3 deg?. This is the size of boiler you needed and existing one could be range rated to this.

 

[kgfx_5]

73 kWh(m2/year)

Confused by the units here but if it's supposed to be 73 kWh/m2/year that is a total annual consumption of 25550 KWh. But what is the heat loss (in KW) at -3 deg?. This is the size of boiler you needed and existing one could be range rated to this.

Yeah, well, in certificate information is shown for the whole house, and whole house is 600 m2. Just a garage and some other areas are not heated. So as far as I get it we are talking about ~43800 kWh/year for the whole house. I am not sure about heat loss, never seen this number anywhere in documents.

 

[gpbeck]

Yeah, well, in certificate information is shown for the whole house, and whole house is 600 m2. Just a garage and some other areas are not heated. So as far as I get it we are talking about ~43800 kWh/year for the whole house. I am not sure about heat loss, never seen this number anywhere in documents.

Can’t see how you could have had a new system designed without a heat loss calculation, which is the heat input it requires. Not annual consumption. Must be somewhere.

 

[gmartine]

Where are you?

Where are you?

 

[John.g]

Can’t see how you could have had a new system designed without a heat loss calculation, which is the heat input it requires. Not annual consumption. Must be somewhere.

You require the Heat Loss Indicator as shown below.
This is my own HLI, heat loss indication, my house is 140M2 so 600M2 based on this only requires a 13.7kw boiler, , I use 12,000kw of kerosene/ 8 month annum, which = a house heating requirement of 10,200kwh.
Even if I based the boiler output on a weatherdT of 23C, (-3/20C) then, a 32kw boiler based on the same HLI of 2.29 woulf suffice to heat a 600M2 house and how often will the temperature be -3C in the UK and how likely will it require the whole 600M2 to be heated??.

 

[kgfx_5]

You require the Heat Loss Indicator as shown below.
This is my own HLI, heat loss indication, my house is 140M2 so 600M2 based on this only requires a 13.7kw boiler, , I use 12,000kw of kerosene/ 8 month annum, which = a house heating requirement of 10,200kwh.
Even if I based the boiler output on a weatherdT of 23C, (-3/20C) then, a 32kw boiler based on the same HLI of 2.29 woulf suffice to heat a 600M2 house and how often will the temperature be -3C in the UK and how likely will it require the whole 600M2 to be heated??.

View attachment 79124

Sorry, should have specified, I am not living in the UK. Our heating season lasts about 200 days and average temperature outside is 1-2 C during these days. Lowest temperature is about -19 C, but it is pretty rare, it can be maybe 5 days per season max, and not every winter. I will look in my papers, maybe I missed something about heat loss. Previous boiler we had here was old 42 kw Buderus.

 

[kgfx_5]

Where are you?

Lithuania

 

[ShaunCorbs]

A buffer would help and you can remove the llh then but you will loose some efficiency did you have a Heatloss done as 40kw sounds big ?

 

[kgfx_5]

A buffer would help and you can remove the llh then but you will loose some efficiency did you have a Heatloss done as 40kw sounds big ?

I am not sure that it is done like in UK here in Lithuania. I checked papers, the only thing I managed to find was the information I provided in earlier posts. I might do some calculations, but I have to find information about insulation etc., have to go through some more papers. Last year heating season I burnt ~4000 m3 of gas, if it matters.

 

[John.g]

4000m3 gas = 44000kwh= 38,720kwh to heating @ 88% boiler efficiency.
How many rads (& rated output) and UFH zones and loops etc & design outputs etc.

 

[John.g]

Is this a low loss header?.

 

[ShaunCorbs]

Yes John

 

[ShaunCorbs]

I am not sure that it is done like in UK here in Lithuania. I checked papers, the only thing I managed to find was the information I provided in earlier posts. I might do some calculations, but I have to find information about insulation etc., have to go through some more papers. Last year heating season I burnt ~4000 m3 of gas, if it matters.

Might be best to see if you can work out the outputs of your rads eg find similar ones in the same sizes they should state outputs etc

 

[kgfx_5]

In the whole house there are 18 radiators, sum of their output at 75\65\20 is ~46.8 Kw. Plus UFH, 3 zones, ~65 m2 combined. On each floor there is a distribution manifold. On the first floor there is also a UFH pump unit. There are also 2 towel warmers, not sure about their output, and 3 small underfloor radiators near windows.

 

[gpbeck]

There will be no condensation at those high temperatures. System should be balanced to produce a 20 deg flow/return drop. Boiler can do water priority (higher flow temps for water heating) so can you not try it at lower flow temp, 55 or 60?