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Viessman Vitodens 100W, dead heat exchanger, DHW box

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pepinbilt
pepinbilt Member Posts: 7
edited February 21 in Radiant Heating
Hey there everyone , 

Let me start by saying my knowledge of boilers is not great, but figured it was the way to go when we built our house.
Construction is 2100sq ft slab on grade, with 800 sq ft of loft. We built in 2015.
Edit:
Boiler is run off of Propane and untreated well water. I don’t believe we need a softener as the water doesn’t seem to be hard. Although it hasn’t been tested for quality 

We had a contractor in town do everything on the heating side for us.
We have 5 zones in our in floor setup, and heating is done via a Viessman Vitodens 100w, it has the Direct Hot water box mounted to the unit.
This system has never really worked great. The water flashes hot to cold while running a shower at full temp, the water will remain steaming hot if not going through a mixing valve (for example taps or a bath with independent taps). We have had this system flushed with no improvement. Local contractor says the DHW heat exchanger is plugged and will need replacement. On the house side, the floors get to lukewarm at best and main living area of the house doesn’t seem to get much past 67.

During this service, a regular cleaning showed the heat exchanger on the boiler had cracks on the outside rim (looks like cast) The tech couldn’t believe the amount of wear, we have had the exchanger cleaned every few years but he is blaming it on lack of maintenance. The Main boiler heat exchanger is now replaced.

Characteristics of the boiler running seem to be pretty good, although in DHW it goes to full fire , water temp up to 190+ and ramps down pretty quickly to about 135 or so It repeats this process a few times in the running cycle for DHW and this was the tech’s best guess at accelerated wear.
now he is torn whether we need to replace the entire DHW, or a control board, or take your best guess and throw money at the thing. Pretty frustrated and looking for some insight that might help
anyone have some ideas?
thanks kindly 

Comments

  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 4,004
    edited February 21
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    Wow! The piping doesn't make sense. There's more going on here then just a bad boiler.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • clammy
    clammy Member Posts: 3,111
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    I believe it never work correctly due to it not being installed properly . The primary secondary piping is not correct a hydroseperator should have been used . As for domestic hot water w well water you would have been far better off w an indirect tank over a plate exchanger they require yearly cleaning as does the boiler . Was the systems combustion set up w an analyzer ? If designed and installed correctly it should work ,putting up w something that does not work from the beginning usually means it shall never work . Was a heat lose for your radiant done to ensure your radiant could satisfy your heat load if not then it was just a guess. . Possibly u may have the wrong installer service guy being he recommending replacement but has he tryed flushing or acid washing the plate . Your heat should be able to satisfy your thermostat if not then there s a design flaw in your radiant either to lower temp not enough tubing poor layout and design and maybe no insulation under the slab or suspended ,staple up tubing . I would gather they never told you it needs yearly attention when they installed and that it will cost ?
    Peace and good luck clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
  • pepinbilt
    pepinbilt Member Posts: 7
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    Can you guys elaborate what is wrong with the piping and give me some insight on that hydro separator you had mentioned?
    im at the point now where im frustrated to the point where I just want to take the DHW box out completely and replace it with a electric tank, the tech says with the kombi boiler the DHW must stay because the system is tied in with each other lol.
    honestly at a loss really 😆
  • psb75
    psb75 Member Posts: 834
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    System built with skill and good components. Bad design.
    Alan (California Radiant) Forbes
  • GGross
    GGross Member Posts: 1,050
    edited February 21
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    In regards to your primary heat exchanger, I have only ever seen them pop a hole in the front when they are not installed level on the wall, usually poor maintenance goes along with this, basically the condensate can pool up at the front cover and eat a hole through it if its not level. If you have a level check it out. Your heat exchanger inside doesn't look too bad, do you have a history of "F4" error codes or any error codes really?

    In theory the tech could disconnect the DHW from the system and leave the box, there is no issue with this, the boiler will just never get a call for DHW, you could also remove the DHW box, add in a boiler pump (the current one is inside the box) and reprogram the boiler to not use the DHW box.

    The heat exchanger has a lifetime warranty to the original owner, (US models ) the DHW heat exchanger is considered a part so generally 5 years for that. If you have someone change the heat exchanger make absolutely sure the boiler is sitting on the wall level, or this will happen again. I also imagine your water may have a bit more hardness than you think, the DHW symptoms you describe track with a scaled DHW heat exchanger. This part can be completely removed and cleaned, or replaced
    clammyAlan (California Radiant) Forbes
  • clammy
    clammy Member Posts: 3,111
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    The spacing on the 2 primary secondary tee is not correct they should not be done w a elbow between them generally it’s a straight pipe on both inlet and outlet of the teess ensuring that there is not much pressure difference ,the other route is more money and is to use a hydro seperators which vissesmann does make there own version of and more information on there purpose and use can be found on line . Generally a hydro seperators are used most who offer mod con installation due to knowing that the system as a whole will function better but on a budget closely spaced tee will surface if done correctly . I can tell from the piping but if your radiant is not coming up to temp possibly your installed may have piped the mixing valve incorrectly . It’s kinda hard from the piping to tell but your pump should be pumping away from the mix port on the mixing valve . Generally I see a lot of mis piped system and they seem to work some what w some complaints on cold days but be assured that if I had piped your system that way it would never work . That’s the law those who have a clue always get bitten while the clueless get paided and it’s ions before the real issues of a poorly installed wall hung rear there head and every states it work while mean while at first glance a pro knows the issues and pretty much knows that he will not get the work being doing it correctly will be more costly then the original problem prone install was but there will be no issues .
    What’s worse is when it was being installed the installer should have been clear about yearly servicing and maintaince and that without early failure would occur ,this is a very common thread w mod cons . Personally I service and maintain what I install unless the customer does not want to pay or get a attitude over maintance in which they never have to worry about hear from me as a courtesy call for yearly service ,I’ll wait till they call usually because of issue like coding off or complete boiler failure in which case I usually say to busy and let some one else hammer them w a replacement .
    As I was told and as it really is . The bitterness of poor quality is soon forgotten after the bitterness of poor quality . Unfortunatly the quality of everything is always being lower a notch or two every blink of a eye so as we see even the mighty big v is the victim of lack of service while I thought that they did just about everything but I guess like every other unit they all need a human once in a while. Ps have some add a voltage surge protection it’s cheap insurance for the electronics .
    Peace and good luck clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
  • psb75
    psb75 Member Posts: 834
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    Voltage surge protection for mod cons and heat pump water heaters is a great idea! I have had quite a few mod cons and HPDHW units with electronics failures this winter due to power outages/surges on rural a electric grid.
    Even better is whole house surge protection. Somebody at tech support recommended that a UPS (back-up power supply) device comes-with its own surge protection.
  • pepinbilt
    pepinbilt Member Posts: 7
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    Thanks for the replies everyone, 

    GGross, the contractor had just replaced our main heat exchanger in the boiler yesterday, he had brought out a new heat exchanger for the DHW as well, replaced it, and had no change. Threw the old exchanger back in.
    he stated there could be blockages elsewhere, could be a boiler computer board failure, yada yada.

    it’s honestly just too bad in the sense that this is our dream home build, was really looking forward to in floor heating, and it’s been a complete nightmare 
  • GGross
    GGross Member Posts: 1,050
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    The flow sensor inside the combi kit sometimes get some "stuff" on/in it that negatively effects performance, they probably already replaced that?

    Use your level to check how the boiler sits on the wall, there will be future problems down the line if its not level. You are fully able to just get a separate water heater and abandon the tankless/combi function. I have this exact boiler in my own house and don't even have the combibox attached
  • hot_rod
    hot_rod Member Posts: 22,150
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    The main thing I see is the mixing valve for low temperature is mis-piped. The circulator should be on the mix port, opposite of the blue knob, maybe the return and supply are mixed up also. That may be the issue with inadequate temperatures. Unless that is an odd valve with the mix port on the side?

    The primary secondary connection is not text book but it will work. Too much restriction between the tees could induce some flow through the boiler when the zones are running but not the boiler pump. That boiler HX has enough flow restriction I doubt any flow goes through it under that condition

    It is salvageable if the installer had a better piping diagram to follow.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    GGross
  • clammy
    clammy Member Posts: 3,111
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    I really think you may need a better contractor possibly one who has some real hydronics piping experiences under his belt including primary secondary piping and piping mixing valves . If the system cannot reach desired temp there may be more wrong w the install then just the piping and the way the in floor is piped it would have never worked had I done it that way .Not to be mean to your installer but they should have had the water tested being it well water and should have at the least filled the system w anything other then your non tested well water being vissesmann has water quality guide lines they like to be followed . From the fact that hydronic piping is not really up to snuff I don’t put to much faith in how it’s wired and if in fact the units been set up correctly including lp gas pressure ,combustion testing ,it’s just question I ask .
    As for the corrosion on the bottom edge heat exchanger I would say from the looks of it that it may have been condensate not draining out over time or as other have said the unit not being level and tilting towards the front or possibly constant cycling on temp from poor piping bouncing on its limits and over time causing that seamed joint and slowly separate
    From the expansion and contraction from as the installer stated boiler wear huh from excessive cycling sounds like Pooh to me but a great excuse to cya on a unit which should have lasted longer which was improperly piped but survived at least for some time .
    Truth be told has to be some one better then what you got ya just got to pay them what they want being ya paid this guy and it’s not really close to being correct .
    Again not being mean spirited just telling it like it is .
    The sweeten of a cheaper price is soon forgotten after the bitterness of poor quality .
    Words I live by ,peace and good luck clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
    GGross