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?

 

[kgfx_5]

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?

Those are just numbers from radiator seller. Right now my boiler is working (when it is working) on 55 C, and it is fully enough for now. I would like to try it on 45, but it just short cycles, never actually starts.
Flow is around 53, return around 38.
——
Hot water is prioritized, there are no problems with DHW.
——
Question - best way to deal with this problem would be buffer tank, boiler change to 32 kw with better modulation, or 2 boilers 25 kw each (worst scenario for me)?

 

[John.g]

Those are just numbers from radiator seller. Right now my boiler is working (when it is working) on 55 C, and it is fully enough for now. I would like to try it on 45, but it just short cycles, never actually starts.
Flow is around 53, return around 38.
——
Hot water is prioritized, there are no problems with DHW.
——
Question - best way to deal with this problem would be buffer tank, boiler change to 32 kw with better modulation, or 2 boilers 25 kw each (worst scenario for me)?

Have you any idea what the primary flow through the LLH is?, assuming it is running above at ~ 12kw, then a dT of 15C means its circulating 11.47LPM , 0.69m3/hr, this primary flowrate is determined by the primary circulating pump setting and is presumably fairly constant through the boiler Hx, the burner will trip at 60C so the boiler output can only rise to 17.6kw before burner trip (assuming boiler return temp remained at 38C). One might think that the primary boiler flowrate might be based on the boiler output and a dT of say 20C, this means a primary flowrate of 35.1LPM, 2.11m3/hr. this would then, theoretically result in a dT of 5C at 12kw output.
But more importantly it means the boiler could fire at say ignition conditions of 30kw without exceeding 50C from a return temperature of 38C, maybe this is why you have to raise the SP to 55C?.
The boiler manual should show the max flowrate recommended.

 

[gpbeck]

If your boiler is pumping more than the system pump off your low loss header this would shut it down. Think I’d try range rating the boiler down to say 20kW and see what happens. Your radiators are probably oversized so are no guide to your actual heat loss. I think I’d do my own heat loss which would give an idea.
Perhaps the best thing would be a heating engineer to visit you and advise.

 

[John.g]

One (good) reason for a LLH is that it allows primary and secondary circuits to operate at completely different flowrates, for example you may have the primary circulating 35.1LPM as above and the secondary only requiring say 3.6LPM, the primary will recirculate 31.5LPM and supply 3.6LPM to the secondary with the secondary returning the 3.6LPM to the primary to give the 35.1LPM primary flow&return?.

 

[kgfx_5]

Have you any idea what the primary flow through the LLH is?, assuming it is running above at ~ 12kw, then a dT of 15C means its circulating 11.47LPM , 0.69m3/hr, this primary flowrate is determined by the primary circulating pump setting and is presumably fairly constant through the boiler Hx, the burner will trip at 60C so the boiler output can only rise to 17.6kw before burner trip (assuming boiler return temp remained at 38C). One might think that the primary boiler flowrate might be based on the boiler output and a dT of say 20C, this means a primary flowrate of 35.1LPM, 2.11m3/hr. this would then, theoretically result in a dT of 5C at 12kw output.
But more importantly it means the boiler could fire at say ignition conditions of 30kw without exceeding 50C from a return temperature of 38C, maybe this is why you have to raise the SP to 55C?.
The boiler manual should show the max flowrate recommended.

Those are some next level calculations for me, lol. I don’t know about flow levels, unfortunately. Right now, for example, I see the picture of boiler that turned off burner and for whatever reason temperature doesn’t drop fast, so this time it managed to heat something. But, difference between flow and return on LLH is 2 C. While there are still 5 radiators open, not including UHF and other stuff.

Manual suggests using 6th position on boiler’s pump that equals 2.8 m3/h when deltaT is 15C? I am not sure how installers set them up. Are those real numbers or am I looking the wrong way?

If your boiler is pumping more than the system pump off your low loss header this would shut it down. Think I’d try range rating the boiler down to say 20kW and see what happens. Your radiators are probably oversized so are no guide to your actual heat loss. I think I’d do my own heat loss which would give an idea.
Perhaps the best thing would be a heating engineer to visit you and advise.

Yeah, I will try finding someone who can help me locally. Regarding range rating, You mean like this?-

 

[kgfx_5]

One (good) reason for a LLH is that it allows primary and secondary circuits to operate at completely different flowrates, for example you may have the primary circulating 35.1LPM as above and the secondary only requiring say 3.6LPM, the primary will recirculate 31.5LPM and supply 3.6LPM to the secondary with the secondary returning the 3.6LPM to the primary to give the 35.1LPM primary flow&return?.

Yeah, but I have only one heating circuit.

 

[gpbeck]

Yes but range rating of 20% would be 10kW which is less than boiler minimum. 40% would be 20kW.

 

[John.g]

Yes, 2.8m3/hr at a dT of 15C = 49kw. Presume this pump is internal to the boiler and isn't one of the Wilos where its very easy to derive their circulation rate from the pump curves?.
Anyway, IMO, the main thing to try and confirm is that the primary pump is set as high as possible, don't think you can do much more than that.

 

[John.g]

Yes but range rating of 20% would be 10kW which is less than boiler minimum. 40% would be 20kW.

Maybe the boiler has been range rated to 20kw (40%) since installation??.

 

[kgfx_5]

Yes, 2.8m3/hr at a dT of 15C = 49kw. Presume this pump is internal to the boiler and isn't one of the Wilos where its very easy to derive their circulation rate from the pump curves?.
Anyway, IMO, the main thing to try and confirm is that the primary pump is set as high as possible, don't think you can do much more than that.

View attachment 79151

Yes, I was referring to internal Viessmann pump.