Viessman 200-W Boiler

jgach11886

Hi, so I have a customer with a Viessman 200-W condensing boiler listed above. He complains when it gets to below 10 degrees outside that it doesn't maintain t-stat setpoint of 71 degrees, its gets to 68 and doesn't satisfy his setpoint.

The boiler doesn't have any fault codes, it utilizes a primary secondary loop piping setup. 3 zones, 1 for each floor of the house. 1st floor they keep it at 65, and 2nd floor is their rooms which is where it won't maintain the 71 degree setpoint. 3rd floor is fine because the hot air rising.

The have lived in the house the last 3 years with this issue, when they bought the house the changed to this new viessman boiler. So they imagine the previous owner didn't live with this issue with the old boiler, so the baseboards around the house shouldn't have anything to do with this issue.


The boiler was modulating as it got demand, it was reading 21 degree outside air temperature. The boiler temperature would vary, but the highest it got up to was 176. I suppose that was when 1 or maybe all the zones stopped calling. The unit does his DHW as well. Its a 125k BTU boiler in a house from the 1970s so its not that old of a house.

I was hoping to get into the installer setups to see if I could change the heating curve, or the aqua stat setpoint or boiler temp setpoint.

Anyone familiar with these boilers?

bulldoglax

This boiler is a great boiler but the smaller sizes have a high limit temp of 176. For this model you won't go higher until you approach the units meant for light commercial.

The problem is people are using these in fin tube installs when it's real selling point is its control and control strategy for radiant, multiple low temperature heating zones as well as tying in modulating or motorized mixing valves.

You should do a heatloss for house but have the use a lower temperature water to design the distribution system. Most likely will have to add additional ft of radiation.

Also if you move set point temp up on boiler it acts as a curve change without getting into coding level one or two.

Paul Pollets

Raise the heating curve. Each .1 increase raises system water temps by 3 degrees. IE, If it's set at 1.4, raise it to 1.6 and see how it responds. Read the manual to see how to change it.

jgach11886

http://www.viessmann.com/vires/produ...VSA00003_1.PDF page 118 are the specifications.

So it says it has a Electronic Temperature Limiter of 82C which is 179.6F (fixed)

Then it says Temperature Limiter setting of 100C which is 212F (Fixed).


So I'm not sure if I could some how change the max water temp/Aqua-stat to 190, I know usually 180 is the max setting it should be, but at 190 i would think it would work fine still as long as it doesn't trip the hi-limit set point which I'm not sure if that would be the 212 in the manual.

I don't have any pictures of the piping arrangement, I'll try to see if the home owner can text me some.

GW

That’s the chink in the armory with Viessmann, what is the temp the boiler is displaying? 9 houses out of 10 can deal with the temps the Viessmann boiler produces.

No, it’s not Viessmann’s fault the home needs 180 or 190 in a cold snap, but if the heating contractor doesn’t get the memo before installing the Viessmann, it becomes his fault

I’ve installed 140 wall hung Viessmanns, I’m sure some here have installed more. I’ve been in tough conversations a few times; it’s not fun.

GW

Ok 176, that’s all you’re gonna get from that boiler

you need:

More baseboard
Or
Less heat loss

Maybe look around and see if all the B.B. are working well; good convention

SeymourCates

@jgach11886

Raise the 'stat setting on the first floor to a minimum of 68F. 70F is preferable. The second floor will likely come up to 71F.

With a 65F setting on the first floor, this zone will operate at a duty cycle far lower than the second floor. Furthermore, the second floor will partially heat the first floor due to the large differential in setpoints.

The boiler has more than sufficient capacity to heat both floors to 71F. Use it.

GW

Indeed Seymour, just lacking the temperature the heat emitter system requires in this situation

EBEBRATT-Ed

Many older systems were designed for hotter water temperatures in some cases 200 deg (190 average). Some of the old books recommended this to reduce the amount of baseboard.

People install a condensing boiler that maxes out at 175 and then are not aware of the extremely high pressure drop of some condensing boilers, most come with circulators designed for a 30 or 40 degree TD instead of the 20 deg the baseboard was designed for. So now instead of 180 or 190 average water temp your getting 155-160 average wt

In most cases because there was fudge in the original heat loss or windows and insulation have been improved it works fine.

Then again not so much with the weather we are having

You have to read the fine print. 10,000btu/gpm =20 deg td
15,000btu/gpm=30 deg, 20,000btu/gpm=40 deg

It sounds real good until you look at the average water temperature dropping. Look at the head loss for the increased flow you will get a surprise. Big pumps

GW

Yes Ed, out of the 140 Viessmann wall hungs I installed, only three installs had me in difficult conversations when the cold snap came. The other 137 I beat the odds.

The topics are:

Total capacity
Rated flow through boiler
Max temperature

Total capacity, it’s hard to goof this one up but certainly possible

Rated flow through the boiler: you may get jammed on this if you’re close to boiler’s capacity UNLESS) your distribution system can work with a larger temp drop. Most retrofit jobs we do aren’t. Most drop about 15 degrees in my experience

Max Temperature: this is what we are discussing when the cold snap comes. Gotta add heat emitter or reduce heat loss. Both is a good answer too.

jgach11886

Thanks for the replys! I did tell the customer about setting the 1st floor warmer, so hopefully this will help.

GW

Yes Seymour is right. We did an oil boiler last week. I set high limit to 180. I email a few days later asking how things are going. He says 1st fl won’t hit 70, just 68. It’s been single digits and zero. He’s not running his sec fl heating. I say turn the dial to 190.

It’s a Perter and Paul thing. The heat will migrate upwards, and the baseboard wasn’t build to do two floors worth of heating

jgach11886

So it turns out in the application guide its not recommended to use this boiler for copper aluminum fin baseboard. It is possible with limitations i believe it says, It would have been ok with big cast iron radiators so the application guide says.

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0ahUKEwiY1OvWkZrZAhXFl-AKHbJiBOEQFggpMAA&url=https://www.viessmann-us.com/content/dam/vi-brands/CA/pdfs/wall-mount/vitodens_200_application_guide.pdf/_jcr_content/renditions/original.media_file.download_attachment.file/vitodens_200_application_guide.pdf&usg=AOvVaw3JeL5W1ESBZqRdQiKy6ETb

SeymourCates

@jgach11886

Be ever thankful you don't have the B2HB. You'd really be freezing. This is the boiler for which they are greatly concerned if procured for fin tube.

GW

It’s good to know