Installing the extension kit on a Vaillant EcoTech Plus 831


How do I wire up the extension kit to a Vaillant EcoTech Plus 831 so that it can use the OpenTherm protocol?

There are no room thermostats connected nor does it have the built in programmer on the boiler.

Have a good Google around and nothing seems to be clear. My boiler has terminals 3 and 4 bridged so that the call to heating is always on, and assume that this is what the extension kit needs to be connected to to switch the heating on and off?

Or should it be wired up to the eBus?

Any help gratefully received 😀

Best Answer


  • Here is the board schematic of my boiler that I have just found if that helps.

  • @guardianangel

    Vaillant boilers normally come only with eBus unless you are in the Netherlands. In the Netherlands it appears to be a country requirement to support OpenTherm so Vaillant boilers come with a Vaillant VR33 module which converts the boiler to OpenTherm.

    Annoyingly even though this is a genuine Vaillant part if you get it fitted here in the UK even by an official engineer it will invalidate your warranty according to Vaillant.

    Also be warned, Vaillant boilers with the VR66 control module are not supported by Tado as apparently Vaillant changed the eBus protocol compared with the VR65 controller module which Tado does work with.

    I have not yet seen any news from Tado that they have managed to add support for the VR66 controller.

    Worst case you could control the boiler in old/dumb 'call for heat' mode and not eBus or OpenTherm. Another suggestion has been to buy an old VR65 module.

    Personally I am avoiding the problem and intend to buy a Worcester Bosch boiler and use its eBus control.

  • @jelockwood

    Thanks for the info. I specifically asked Tado whether my boiler was compatible with Tado before I bought it and they said yes it was. So it is on them to get this working.

    But you mentioned setting it up for call to heat (which it has the jumper fitted so that is always enabled). How would one setup the Tado extension kit wiring to do that?

    Thanks in advance.

  • @02_london

    Many thanks, I will give it a try and report back.

    Just to clarify, when you say "and dont forget the link wire in 24V RT (boiler side)", that I think equates to pins 7 to 9 according to my diagram above? I don't currently have a jumper on any of those terminals, so do I need to add one, and if so between which ones?

    I also currently have a call for heat jumper between terminals 3 and 4 on the 240v side, do I need to remove that?

  • OK so thanks to the guidance of @02_london I now have this working. On top of the instructions in the PDF he shared above, I needed to do the following:

    1/ There was not currently, nor was it needed, a jumper for the 24V RT on the boiler side.

    2/ The jumper between pins 3 and 4 on the 240V side which I already had fitted needed to remain. This is not shown in the board diagram in my earlier post but is used to permanently enable "call for heat".

    It was just a case of connecting the eBus + and - terminals on both sides. My Extension Kit was already at the right patch / firmware level for this to work.

    Hope this post helps someone in the future.

  • Hi Guardianangel

    Glade you got it working, I suspect you didn't need the 24V RT pins 7 and 8 link wire as you already had the 240V link in place. Link wire keeps the boiler on and our eBUS tells it to turn off to tado requirements.

    Regards James

  • I’ve got a bit of a dilemma on my hands. I bought a Tado on a Black Friday deal in preparation for my new boiler being fitted in the weeks after it, however my local heating engineer who installed my new combi boiler - Valiant Ecotec Plus 832 was unable to get the Tado extension kit working with the boiler via the ebus(they’re all connected to the internet bridge ok). He spent 2 hours trying to get it all working, even going to the lengths to call up a Valiant rep and they done some diagnostics and it came with some ebus error on the screen and a small spanner icon - that’s when they both decided to give up. So now I’m left with a nice new boiler and no thermostat to use with it(resorting to manually turning the boiler on /off and making temperature changes throughout the day), despite Tado claiming to have support. I stumbled across this issue and was hoping someone could give me some pointers with the thin hope that I can have a try at making it all work before sending the Tado kit back in the hopes I can get a refund. Any help you can give me will be much appreciated, I've attached a few pictures below.

  • @dnic

    It could be your issue is the same one I cautioned about to guardianangel.

    Vailllant have apparently changed their eBus protocol with their newer VR66 controller module compared to the VR65 controller module. The Tado system works with the VR65 but not the VR66.

    Your options are as follows.

    1. Find an older VR65 module to replace your VR66 module, I have seen them listed on eBay but you might want to discuss this with your boiler engineer
    2. Get a VR33 module, this translates the eBus commands to OpenTherm commands which Tado also support, the VR33 module is a genuine Vailllant part and fitted as standard to their boilers in the Netherlands but will invalidate a UK warranty despite this
    3. As done by guardianangel configure the boiler to run in 'call for heat' mode

    I still hope that Tado will eventually upgrade their software to add support for the VR66 but this might require them either buying a new one to reverse engineer or Vaillant releasing new documentation. (The later is sadly unlikely I feel.)

    In my own case I plan to get a Worcester Bosch boiler instead. This also uses eBus. The following is a link to a reseller for the VR33 module, they are mainly sold by Netherlands resellers due to their being required in the Netherlands and not supported by Vaillant in other countries. However plenty have people have ignore Vaillant.

  • Looks like you have the correct firmware on your extension kit 64.6 Thats great, now follow the steps below:

    You need to have your Smart Thermostat paired and your extension kit paired with bridge and you can see them in tado app or webpage under SETTINGS | DEVICES - Other Devices (if they are still in setup get tado to move them to Other devices basically informing them all wiring is done, tado will then move them to Other devices.

    1. follow pages 16 to 19 (of the attached) to configure your smart thermostat (use D07 Standard Vaillant eBus )
    2. Then connect vaillant BUS + and - (boiler side) to the + and - on the MAX 36V DC side of extension kit

    There is no need for L and N on extension kit as it gets its power from eBus, jumper link can be set to ether, it doesn't matter which way its round.

    If you need further help leave me a contact number or email and ill get in touch to explan over the phone, Its really simple once you know the procudure of which took me 4 to 5 days with tado support.



  • You also could do away with the Extension Kit and just connect the Smart Thermostat MAX 36V DC + and - to boiler BUS + and - as we have combi boilers where hot water is always on.

  • Thank you both very much for your help. I *believe I have it working* using @02_london's instructions above. The only reason I say that is because it seems to take a long time between issuing a command on the mobile phone app and the boiler doing anything about it - is this normal?

    I have a few other technical questions if you don't mind:

    1. Currently I only have + - in the max 36V DC side of the extension kit, is that all I need plugged in there?
    2. I still have the jumpers in Burner off and 24V- RT - do I keep those in there?
    3. The smart thermostat itself seems to have different icons now when I press the button, and I'm not sure what controls what?
  • @dnic @jelockwood

    My installation using eBus works as per the instructions detailed by 02_London further up this thread, but I have an 831 and not an 832, and your circuit board is a different layout.

    However, @dnic looking at your photos, you have the eBus (grey and black wires) wired up to the 240 side on the extension kit which is wrong. You only need to go from the eBus +/- on the boiler to the +/- on the extension kit. This is a low voltage feed that will power the extension kit and also carry the protocol as well. There is no need for the 240v line and neutral feeds. Overall you only need two wires out of the four.

    Just as a side note, if your plumber wired up that extension kit I would never have him in your house again. The line (brown) cable has half the strands hanging out, and if he does not know the difference between a 240v feed and the low voltage eBus feed then he is a chancer. If he had got that wrong the other way around that extension kit would have gone bang.

  • @dnic

    1/ I cant really answer for your boiler as the main board is different to mine, but I had a jumper on the 240v side which permanently enabled the "call to heat" function on the boiler, so when ever I turned up the thermostat dial on the boiler itself, the boiler fires up. This has not been removed, and is needed to enable eBus to fire the boiler when it needs to. In my setup, I only have the +/- wired up on the extension kit (and this will be the same if you wire to the thermostat directly), and this is in turn wired to the eBus +/- on the boiler side. Only two wires are then needed when wiring up the Tado system. You don't need any feeds or wires to/from the 240v side.

    2/ You will find a delay between changing settings on the app and the boiler reacting. Typically this can take about 30 seconds, so it is normal. As long as it is doing what you expect it to do then don't worry about it.

    3/ What icons are you seeing? Can you post up some pictures?

  • @guardianangel

    However, @dniclooking at your photos, you have the eBus (grey and black wires) wired up to the 240 side on the extension kit which is wrong. You only need to go from the eBus +/- on the boiler to the +/- on the extension kit. This is a low voltage feed that will power the extension kit and also carry the protocol as well. There is no need for the 240v line and neutral feeds. Overall you only need two wires out of the four.

    I did notice this, now I have only the grey and black wires going between eBus +/- on the boiler and the MAX 36V DC +/- on the extension kit and removed any other ones that were plugged in and covered them with electrical tape to stop them from coming in to contact with anything else. Thanks for confirming that I did the right thing with this 👍️

    Just as a side note, if your plumber wired up that extension kit I would never have him in your house again. The line (brown) cable has half the strands hanging out, and if he does not know the difference between a 240v feed and the low voltage eBus feed then he is a chancer. If he had got that wrong the other way around that extension kit would have gone bang.

    Your spot on with that one, I came to the same conclusion after he left me without a thermostat, blamed Tado and left the boiler with an error on the display(I think removing the 240v brown and blue wires made the error icon disappear) he's never setting foot in my house again. I'm tidying up this wiring myself!

    I'm still at work, but will give some more info and post some picstures a bit later when I'm home, but in regards to the delay I mean like 10 minutes. My internet is also very good at home(300mbps+) across Google wifi mesh so I can't see that being the issue.

  • All worked ok for me on an 835 which has the same circuit board as @dnic

    I still have the 240v supply running via the extension kit as that it how it was wired but all works ok. Have tested via the thermostat and a TRV and heating comes on each time.

  • Thanks for the info folks, works perfectly on my 18 month old 838, which has the same style board as in the pictures ‘ dnic’ uploaded. Just have the bridges in the 24V RT and the burner off terminals.

  • Hi All,
    Installed the Tado starter kit yesterday. Smart thermostat, extension kit and internet bridge.
    I have a vaillant 838 and was using a built in SALUS RF receiver.
    I’ve left this receiver on the front panel and have connected the extension kit to the - and + on the bus terminals however the boiler is not being controlled.
    I’ll ask support when they’re open but do we expect this to not be working because I am running the 31.13 firmware on the extension kit and need the 64.6 to work with my boiler?
    Thanks in advance.
  • SKD
    edited November 2020
    Hello @bkehoe - can you please tell how did you connect your boiler to the wireless receiver ? I have exactly same configuration on my boiler as yours. Did you just open the 24V RT bridge on the boiler and connected it to the 30V ports on the wireless receiver, or something else? Many Thanks.
  • Read this thread with some interest and it made me wonder if my Vaillant Turbomax Plus 824e will support modulated heating if I add a VR33. Anyone know if this will work?
  • @mindstorm , you said you had no problems with your ecotec 835. I’m currently trying to connect to an 835 and having issues with the boiler turning on but not off.

    Did you just connect the black and grey wires to the 240v RT, as per the instructions?

    The instructions Tado sent through don’t mention connecting to the Ebus or linking any of the other connections on the boiler.
  • bashworth81
    edited January 10

    I have an ecotec plus 831. eBus + and - on boiler connected to 36V DC + and - on the extension kit. I have to bridge terminals 3 and 4 like @guardianangel did otherwise the heating doesn’t come on. But then it stays on always. In fact, I don’t think the extension kit is controlling the boiler at all.

    edit: I’ve gone back to the non eBus way of connecting things and my heating is working again. I’m not sure my boiler model supports eBus although the extension kit installation instructions say to wire it up that way.

    its a shame as the temperature seems to overshoot a bit now and I like the idea of modulating the boilers output.

    anyone else experiencing this?

  • @bashworth81

    As I said in your message, since installing on the eBus it has worked perfectly, and is able to modulate. I have even added the Tado TRV's since and they work well also.

  • Thanks for your reply! Let’s see what support has to say. I do wonder if terminals 3 and 4 should be bridged as that made the heating just be on constantly on my system.

    I have feeling it’s software related and I’ll give it another go rewiring when it’s slightly less freezing ;)
  • @DM5

    Sorry - had missed the reply. I've got the connections onto the eBus connector and have then changed the Smart Thermostat settings via the Engineers Menu. @02_london posted details in December. When mine was fitted, it wouldn't turn off on the eBus until we had worked out the changes needed on the Thermostat.

    Although this is copied from the thread - looks roughly like this.

  • This is all very interesting.

    @mindstorm - can I confirm - you are using a tado with ebus and some traditional heating controls using the 230 volts?

    Has anybody else got more than one extension kit connected?

    Currently, I am using an extension kit to do my underfloor heating and would like to install another one to control my s-plan radiators & hot water.

  • Hi @RhoadesBrown

    Just picked this up. At the moment I have the extension kit wired to the ebus connector so using 24v. This seems to be the way to get the boiler to modulate correctly. I then have a wireless room thermostat and two smart TRV's.

    So far happy with how it works, just wish the TRV's were quieter.

  • Just seen this thread and I'll admit to being confused if my system will work with Tado.

    I'm buying a new build with the following:

    Boiler - Vaillant ecoTEC Plus 624

    Cylinder - Vaillant UniStor 300 Litre

    Programmer - Honeywell

    Heating Zone Valve - Honeywell V4043H1056 x 2

    Hot and Cold Water Valve - Honeywell V4043H1056

    TRV's - Drayton RT212

    None of this I can change until after I move in so looking to ideally buy

    1 x Starter Kit – Wireless Smart Thermostat V3+ [Hot Water Control] 

    18 x Smart Radiator Thermostats V3+

    To allow me to control each radiator independently and link it all to my Home Asst install.

    Any advice and guidance would be hugely appreciated.


  • This guide has been useful for me, thank you all for posting. Just waiting on my firmware install to complete ( taking hours) and I can test the system