Vitodens 100w b1ke-199 DHW temp not respected
I have a new Viessmann Vitodens 100w b1ke-199 combi-boiler (DHW + Heat supply for 2 hyrdonic air handlers). This is all < 1 year old.
Ever since we got it, the DHW hot water "scalding hot" (hurts your hand). I got around to setting up ViCare and set my DHW to 115F. When neither the DHW or Heat are being pulled, the ViCare app shows ~115 to 130F for DHW. However, when i start to draw hot water with EITHER DHW (ex. running bathroom faucet) or the heat supply - i can see in the app the temp fluxuates between ~ 115F and 140F, usually staying closer to top 140F range (which is that "too hot" temp).
In the ViCare app, i have a DHW schedule (5:30am - 10pm) and Operating mode switch (DHW) = Standard.
Any idea what could be causing this and how. i can adjust it? This seems like it should be a trivial setting.
Comments
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First thing I would check is if there is a mixing valve under the unit? When these run hot in space heating they have no choice but to overtemp the DHW, a mixing valve is required in my region for all combi boilers for this reason.
next would be to check what the temp is actually coming out the faucet at. I dont use the vicare app much but the DHW matching exactly with the space heating temp is a little odd. is the DHW scalding you when it comes out of the faucet?
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Have you called the person or company that installed it? Or did you install it yourself?
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 slab0 -
yes it’s scalding coming out - I measured at 136F just now
I’ll check for a mixing valve but will have to look up one looks like.
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GC had his sub install it. My GC turns out generally doesnt have very good subs - and isnt eager to take accountability — trying to self educate before going back to him
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it will be a 3 way valve, likely with a plastic cap to make adjustments, and sometimes they have a temp gauge on the outlet (but not always) typically if the temp in the boiler from space heating were overheating the domestic it would cool off after a short while. if your system makes high temp water for space heating you would need a mixing valve (regardless of codes etc) if the system is all low temp (in floor heat) you may also have something wrong with a sensor in the boiler, though it does seem to be reading the temp correctly on your app.
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I’m going to try to remember to check it out tomorrow and look.
I have 2 hydronic air handlers and baseboard hot water heat. I have 4 showers and 6 bathrooms, 2 washers and 2 dishwashers in the building. (2 units) all powered by this single b1ke-199.
after doing some more reading of the manual it sounds like it might be underpowered for this, and needs a buffer tank..? And there’s other models more suitable for the number draw points.. this wouldn’t be causing the DHW temp be ignored right? Also, I have a warning in the app I have lead break for my outside temp detector so it can’t tell the outside time.0 -
no too much draw won't increase the hot water temp, it would actually decrease. so you can get around 4.7GPM constant flow at 120 outlet (depending on your cold water temp) as you go over that flowrate the water temp will reduce. You would find a bunch of different opinions on what unit is best suited for any application, personally I never try to sell someone a combi, I prefer a tank for DHW.
What will cause water to be over temp is if the boiler is calling for space heating at max temp, going over that temp, and then you get a DHW call and the boiler water will overtemp the DHW because the supply water is already too hot.
the outdoor temp sensor I would be curious to see if it is wired in at all. one thing I see people do is set them up with outdoor temp, never install the sensor, and then the boiler will always call for heat as though it was 32f outside. one downside to this is the boiler will maintain that temp in the summer (because it is in freeze protection mode), so you want to either install the outdoor sensor, or set it up properly as an on/off fixed setpoint boiler. this is only slightly related to the DHW over heating.
some pics of the install, far enough back so we can see everything, might help
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here’s some pics:
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There doesn't appear to be a mixing valve on the domestic side. If you were to run the fixture that overtemps the most for an extended amount of time, or run multiple fixtures for a while, will the DHW temperature go back to a somewhat normal range?
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Took some app screen caps running 2 faucets on hot (see imgur below). The temp spiked to very hot (130s-140) for the first ~1 min, then it dropped way down .. lowest i saw on the app was 109F, ratched back up to low 130Fs .. and settled at ~112F; the app showed 112F for what i think is 2-3 refresh cycles.
I put an instant (cooking) thermometer in the flow from the kitchen faucet, and it was inline w what the app was showing in terms of general temp/temp movement.
As an aside - when i took the pictures - i poked around the on-device LCD, and i saw "scald protection" was set ot on … however 140F (which DHW will deliver) is seriously hot to the touch; not sure what it considers scalding.
https://imgur.com/a/7LAaILB0 -
I have a similar problem where my thermostatic showers fluxuate in temperature quite a bit (which is ironic considering the showers have thermostatic valves, but apparently cant keep up w/ these fluctuations).
In general, would you recommend installing a buffer hotwater tank for DHW? Or just a thermostatic valve? Or both?
At that same time — It seems bizarre that the DHW temperature setting on the Vitodens is seemingly completely disregarded. What's the point of even having this setting if the unit can't respect it.0 -
What I would do with this current install is add a point of distribution thermostatic mixing valve. It may take just a little tweaking between the mixing valve setting, and the boilers outlet temp settings to get it right for you.
unfortunately if the boiler water temp is much too hot there isn't any way built into the boiler to prevent the temps from getting too high. this is why you will see a mixing valve for the DHW side on all their drawn combi applications. Viessmann doesn't require it for every install and instead leaves it to local code officials. this is because when the boiler is setup with outdoor reset and functioning below its max setting, this issue really doesn't come up. Once you know that between the combi, and the mixing valve, the hot water doesn't get too hot, then you can investigate the shower valves, they may be scaled up a little.
I usually don't recommend adding a tank to a combi to fix this issue, it can be done but you would need to have external controls to monitor tank temperature, and a stainless or bronze DHW pump to just circulate between the boiler and tank. you would also very likely need to maintain tank temp above what you want and still need to add a mixing valve. I think now that the install is done, the path of least resistance would be to add the mixing valve
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Thank GGross! Super helpful.
- Given the max DHW im seeing (140F) i expect a mixing valve could reliably bring that down to 120F - safe assumption?
- My DHW swings wildly (from ~105G to ~140F) .. Would the mixing valve's effects prevent the swings on the lower end of the spectrum? For example, If im showering I want consistent 120F hot water reaching my shower valve. I dont want water fluctuating between 105F - 120F hitting the shower valve (since when the waters 105F my shower will max be 105F). How does the mixing valve keep the Viessmann from swinging the temperatures? Or would i need to up the DHW temp to be +10F on whatever i want the my DHW to actually be (since that appears to be how far it "swings down") — so in this case set to 125F and set the mixing valve to 115F. Also, are there smart/wifi mixing valves - my mechanical room is annoying to get to (have to go outside, around the house; sucks in the dead of winter - i really like being able to check/control from my phone :))
- Sounds like i need to get my outside temp detector installed.
- Im so confused as to why VIessmann even has a DHW setting if its not respected (on either side! it will go lower and higher!), and/or the "scald protection" setting. Neither of these seem to actually work.
- Curious; what's that grey tall rectangle in the middle of your picture? I dont have one of those from what i can see?
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When your boiler temperature, the water currently in the heating system of the boiler, is so hot that it well exceeds what is required to heat your DHW to the desired temperature the boiler has NO WAY to stop that from happening. its not that the boiler doesn't respect the setpoint temp, the installer did not respect the installation requirements. the boiler cannot break the laws of physics, to cool off the boiler temp you would possibly be waiting 15 minutes with no heat or hot water for the boiler to cool off. that is why you need a mixing valve in your circumstance. With the outdoor temperature sensor programmed but not hooked up this will occur year round, the boiler will maintain max temp because it thinks it is 32f outside, it will do this in July, it will do this when there is no call for heat, it will continue to waste fuel, unless the outdoor sensor is either correctly programmed out, or hooked up.
temperature hunting can be caused by a variety of jobsite conditions, very low flow and the unit might go off on limit, giving you a cold water sandwich effect, too high space temp setpoint and the start of your hot water will well exceed the setpoint. Plumbing issues, scaled up valves, inconsistent well pressure, and the boiler will turn on and off with the rapidly changing flowrates it detects. for these reasons I personally prefer a tank of hot water and not a combi or tankless.
Yes with a mixing valve your DHW setpoint on the boiler will need to be a little higher than outlet temp you desire from the mixing valve, there may need to be some tweaking to get this right.
I can't guarantee you get a straight consistent temperature out of your shower after this change, you may have issues in addition to the scalding issue. However the scalding issue must first be resolved to pursue any additional issues, which may be related to the plumbing system or the shower valves as much as it may be related to the boiler or install,
The grey box is a "low loss header" or a hydraulic separator. among other things it separates the flowrates in your heating system so the boiler always gets the correct flow, and the system gets the correct flow. It is nice, but not strictly required, and your system has an acceptable alternative in the form of closely spaced tees.
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Gotcha - ok, my plan of action is
- Install outside temp detector (looks like i have it, just wasnt installed)
- Install a mixing valve
- Tune the DHW
And see how that works .. if it's still bad,
- Install a tank hot water heater for DHW
- Use the vitodens only power the my HVAC heat (baseboards and 2 x hydronic air handlers.
Im curious if this will help w my poor water pressure on the 3rd floor showers (along w the temp swings) - im 72PSI coming in off the street, but it has to go up 4 floors (basment to third) so not sure if its a PSI or flow issue up there.
Thank you GGross. I cannot tell you how much help you've been! Ill remote back with what I tried, worked, didnt work!0 -
I would hold off on installing anything once the mix valve is done. The mixing valve is going to be there to basically set a high limit for your DHW. If there are additional temp fluctuations it is possible you have a plumbing issue, pressure issue, or some other issue.
The 3rd floor pressure issue is almost certainly playing a role in the temp fluctuations and is very likely unrelated to the boiler or (lack of) mixing valve if you are getting pressure fluctuations along with the temp fluctuations those 2 things go hand in hand. higher pressure means we are moving more fluid through the combi you would see temp go lower when you have a pressure spike, then the boiler ramps up to meet this demand, pressure drops and the water overshoots a little.
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if the mixing value does work, is troubleshooting the temperature (and pressure) fluctuations typically something a plumber would do? a HVAC tech? both together (that will be fun too coordinate :))
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to be honest its usually something they both squabble over whos job it is lol. Best bet is to find a tech that does plumbing and heating. There are numerous things that can cause temp issues on tankless and combis, irregular pressure, plumbing crossover, "junk" getting into the unit, anything that impacts flow, and then of course you have the entire boiler portion. I would expect the boiler to be in good condition as its new.
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