Tado V3+ and Viessman Vitodens 200w
Yesterday my plumber installed a new Viessman Vitodens 200w.
The old one that got replaced was a buderus unit with a Buderus RC35 thermostat unit. (Connected by 2 cables to the boiler)
Today I've been trying all day long to get the Tado V3+ to communicate with the Vitodens.
On the Tado side I connected to the +/- pins. On the boiler side these two cables go to pin 5 and 6 on the KM-bus. On the other Viessman inputs there's a weather temp and water heater.
Afterwards I tried all the settings in the tech menu on the Tado. D0 for opentherm, no success. D37 for Viessman, no succes either.
What am I missing here. I tried everything I can think of. Only thing I did not try was editing some tech parameters I found in the Viessman manual because it's unclear to me how I should find these.
My plumber is not familiar with all these details. Viessman doesnt reply and Tado support doesn't seem to know what the problem is.
Can anyone help me out?
Answers
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Hi.
Sounds like you're looking to run the 200 with Tado's Opentherm?
While I don't have quite the same set up as you, I believe that unlike the new 100, the 200 doesn't play nicely with Tado load compensation. However, I'd suggest you don't need it.
The V200 is among the very best weather compensating boilers on the market. You should be able to set the flow temperature curve so precisely that you don't actually need an internal room stat at all (including night set back through reduced flow temp).
You could use Tado in relay mode, but really only as a switch as to when to turn the heating on/off overall because if you've precisely dialled in the curve you want the boiler - not Tado - modulating the flow temp (I think the v200 has a huge 20:1 modulation ratio, so can still run its burners down to around 1-2kw).
I have an older v100, which has more basic weather comp. I have to pair it with Tado in relay because I can't tweak the curve exactly and so it will eventually get warmer than I need, so I let tado relay 'modulate' from then, and also use IFTTT to turn off the system at night, then back on when it hits a (slightly lower) temperature floor. That said, the system is currently running constantly from about 2:30am to around 9pm, then Tado is taking over til about 11pm. I also use IFTTT to effect warm weather shut down (so the system turns off completely when it's mild outside, rather than circulate cool water).
That's all for context though, with the v200, you shouldn't need to do any of that. Try putting Tado in relay, set it higher than you want the room temperature (say 25c), dial in the v200 curve so that at both cold and mild conditions the desired space temperature is just achieved (and no more). Set a night setback flow temperature. You'll likely find this is the most efficient way to run the system, is incredibly comfortable, and quiet. Also make sure the system is correctly balanced and you're not zoning (e.g. using smart TRVs) - you need the maximum emitter surfaces for weather comp to work effectively and efficiently.
If you use Tado load comp (Opentherm), you'll maybe get the same results, but the system will be reactive rather than proactive (reacting to inside changes rather than adjusting as outdoor temps change before you notice inside), and susceptible to indoor temp changes where the stat is located (busy room, solar gain, etc) that will cause other areas of the house to feel colder.
If you attempt to use the v200 with tado in relay mode for intermittent heating (so using set back temps at night and when out), you'll find you need to set the v200 flow curve higher to compensate because it will need to reheat the space from cooler - at best, you'll negate the intermittent heating gains, but more likely, you'll just have a colder home.
Hope that's helpful
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Hey DM932187
Thanks for the reply. I won't use the Tado in relay mode as this seems counter productive. So if I'm understanding correctly I don't really need the Tado system at all because this V200 is already quite good at managing itself, right?
If so, the only other thing annoying me is the lack of a physical thermostat in house to check what the room temperature is. I like using apps, but sometimes things just need to be simple. In this I case the Tado thermostat would be a handy tool in the living room. Is there any other modern thermostat unit available that just easily works with the V200? I came across the Vitotroll 200-E but that looks more outdated than my old Buderus RC35. :-D
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Ok, I received this reply from Viessman customer service, just in case someone is having the same problem I'm having:
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"If your boiler is from August 2019 or later, the tado will not work ideally with your boiler.
You can use TADO on older boilers, we have a special Viessmann package for which the tado can work perfectly with the heating boiler."
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In other words, they blocked the KM Bus for other brands. Funny enough Viessmans & Tado keep on promoting compatibility in all their manuals and online promo, which is very annoying to say the least.
Big thank you to the Tado support team, for not helping at all and not knowing their products :-)
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@JMCSN - correct, as @GrayDav4276 says, V200 in weather comp will likely be far superior.
When you ask for a modern thermostat that works with the v200, what are you looking for? Any relay stat will work with it (to switch it on and off, or neither if you just set it higher than the flow temp from the boiler can achieve), but I'm guessing you're perhaps still looking for modulation through load compensation?
The only improvement you'll make on the v200 weather comp performance is internal feedback, which will constantly tweak the externally set flow temperature to match the load. I suspect that's likely to be a Viessmann controller as it's all part of one system. Probably a question for Viessmann,
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