Taco and Viessman Vitodens 100


I have a Viessmann Vitodens 100 and it has been running off a Delta More wireless thermostat for a couple of years.

Today I purchased a Tado V3 heating and hot water thermostat kit and also a number of Tado smart radiator valves. The valves are on back order so I thought I would switch the existing wireless thermostat to the new Tado one whilst awaiting the radiator valves

The previous receiver was wired into live and Neutral and then one wire into '1' and one wire into 'L' on block 96 on the boiler. I have wired the Tado exactly the same

The issue I have is that I can turn the boiler on by increasing the temp on the App or the wireless device but I cannot turn the temp down. When I go into the App and click turn off it just stays on.

What is the correct way to wire this up into the boiler taking into account I will be installing multiple Tado smart radiator valves when they arrive

Thanks in advance


  • What did the app tell you to do when you did the install?
  • It said Tado Come to Boiler L and Tado No to boiler 1

    This is the same as the previous wireless device and is exactly as I wired it.

    I can turn temp up with wireless thermostat and with App. I cannot however turn temp down with wireless thermostat or App

    Most bizzarre

  • It sounds like a configuration error in that case. If you download the Tado pro app it should tell you if everything’s working.
  • Thanks. Will download it now

  • Ok so I used the pro app and oddly this tells me it is recommend to connect using OpenTherm D01 which is not what the install App told me to do?

  • johnnyp78
    johnnyp78 ✭✭✭
    edited November 2022
    Is it a combi and do you have the eu version of the wireless receiver? If not you will have to wire it relay - it is better to use a modulating connection if you can but you won’t be able to if you have a uk model.
  • Hi,

    It is a Combi Viessmann Vitodens 100w B1KA

    I have now installed the radiator valves and it seems to be working ok.

    Couple of questions

    1 - As I have smart radiator valves on all radiators should I disable the wireless thermostat as I believe this may be causing conflict issues

    2 - Back to the Opentherm comment my boiler instructions state it fully supports open therm. I am not sure of the benefits of this over relay and also wouldn't have a clue how to wire it in Opentherm as the Tado instructions do not indicate how

    Any help greatly appreciated

  • Tado will definitely give you instructions on how to wire for Opentherm but as you have the uk version there isn’t much point as it doesn’t have digital connections.
  • Hi,

    I have downloaded the boiler manual and it does do Opentherm but as you quite rightly say in my Tado unit I do not have + and - which is what I need to wire it in opentherm.

    Odd how the UK one doesn't have these terminals

  • Oh one final question.

    As I am just using the radiator thermostats do I set it to no zone controller ?

  • Set what to no zone controller? Any room you want to be able to call for heat should have a zone controller, which should be your wireless receiver.
  • Just noticed in the menu you can select the zone controller or select no zone controller.

    I had assumed that having just smart radiator valves that setting no zone controller would be ok but I assume not lol

    Johnnyp78 - Thanks for all the responses in helping me get this up and running, really appreciate it

  • No worries. You would set the zone controller to independent if you had a room where you wanted Tado to open the radiator valves without calling for heat from the boiler, perhaps a room you don’t use much but still want to get some heat when the boiler fires up for another room.
  • @johnnyp78 question regards your last post.

    so if i set one room to independent (i have 1 tado radiator thermostat and 1 wireless thermostat in this particular room), and then set the temp to 20. it always displaying the tile as 'heating to 20'?

    i'm assuming this is fine because as it's independent now, it has no way of actually firing up the boiler?

    will this cause the stats to be incorrect under the tile Care and Protect?

  • The room will say ‘heating to 20’ until target temperature is achieved but won’t call for heat. It will affect the stats , Tado counts any zone controller independent room as heating, even when it’s just opening a valve.
  • Hi Johnny . Back with more questions

    It's all set up and working, however if I set some of the bedrooms that we do not use to frost protection they are still heating up to within 2 degrees of the rest of the house. No idea why

    Additionally, I have managed to find a wired EU version with Opentherm. It comes with a plug and of course needs to be wired into the boiler (X21 on my Viessmann). If it has to be wired to the boiler and also plugged in then it must have to be located in the boiler cupboard (my boiler is in a cupboard) which is a little odd as it will be very hot in there?

    Again thanks for advice in advance

  • The first part sounds like the rooms don’t have a zone controller - you can check in settings - rooms - click on room.

    You can use either the boiler to power the wireless receiver or an external power source, whichever is easier.
  • The EU one states hard wired with a plug
    Maybe I could cut the plug off and wire it straight in
  • Also just checked all rooms and they do have zone controller assigned.
    Maybe the trv could be on the wrong side of radiator although I assume they are bi directional
  • It definitely isn’t hard wired with a plug, there are l and n terminals. It may come with a lead already screwed in, but would just be a matter of unscrewing it.

    You could check if your trvs are properly mounted or if they’re out of range of the bridge, that’s all I can think of with your bedroom issue.
  • Thanks yet again for your help