Help with changing wiring of existing tado installation


I've been a tado user for many years and have been very happy with it.

My initial setup was as follows:

Glow worm Flexicom 30sx boiler

Horstmann H37XL controller

3 x wired mechanical room thermostats, split over 2 heating zones (1 in 1 zone, 2 in another)

Hot Water

I now have:

3 x Tado wired thermostats

Extension kit

5 x radiator thermostats

I think like a lot of people, given the current energy crisis, I was reevaluating my heating setup and I've just become aware that my boiler has modulation capabilities. I've been using it and tado in a simple switched live on/off system this whole time. Doing some research it seems tado have engineered compatibility with the glow worm eBus system, meaning I could wire it in such a way as to use this and the modulation capabilities.

Firstly, is this actually possible? If so, I'm hoping to get some advice on how to wire this up

Attached is the wiring on the extension kit. Back when I first did this, I was on and off with support so I'm going from memory. Since it is only a 2 channel kit, I had to wire both heating channels into one. I used a terminal block as it was difficult doing this otherwise. I wired HW as normal. However for CH, support told me to put a jumper between the CH and L (hence the wire going from the terminal block to L)

Is it possible to change this wiring to eBus? I expect the boiler would also need to be changed but I'd likely get a plumber to do that. What changes would I need to make to the extension kit?

Any advice/guidance appreciated


  • It isn’t really possible to have modulation with a system boiler, except with some vaillant controllers I think. However if you switch to a combi that supports Opentherm or ebus, you will need to wire N L and the two + and - connections on the far right.
  • Thanks Johnny

    Forgive my ignorance. I was going off of this, pages 38/39 (screenshots below) which seemed to suggest this boiler has ebus or mains wiring options? The same doc mentions several times that "These boilers are fully modulating"

    Various threads on the community suggested it was possible to wire tado to control glow worm ebus. For example: and

    Although nothing specifically for SX models

    Is it that it is not a combi boiler? Again, please forgive my ignorance

  • Just another thing, supposedly there is an add-on that you can buy from The Netherlands which turns the ebus into Opentherm compatible but I can't confirm if it works with my boiler. Given it costs ~60e I'm not sure if I want to take the chance

  • I would think you essentially have the same model as a combi, however as you have a hot water tank yours is a system version. Hot water needs to go into the tank at a much higher temperature than it goes into the rads with a modulating boiler, partly so it can stay warm in the tank without needing to be reheated and partly because of legionella risk in standing water below 60c. If your system is clever enough to overcome those obstacles than you should be ok, but I know of hardly any system boilers that can.
  • The Opentherm conversion from the Netherlands would only be needed if Tado can’t support your boiler’s ebus- you should be able to check compatibility with Tado.
  • Thanks again Johnny.

    Seems strange they would offer this feature in a system boiler if it increases risk of legionella

    Having said that, I sometimes wonder if I heat up the tank above 60 often. It's usually on for 1.5 hours a day with the stat on the cylinder set to ~65c but I'm not sure if that is enough time to get it up to temp

    Is it possible to have a hybrid type model do you know? Modulating for heating and unmodulated for HW?

  • Just found this:

    Page 30 seems to address your concerns but seems it only works with 1 water and 1 heating zone (see below)

    While I do have a stat on the cylinder, I don't think it is connected to the boiler directly but rather to the motorised valve

    Looks like I'll need to get a good plumber in as I'm not sure if my system could work even with glow worm's own control options.

    Was hoping it might be a relatively simple change but starting to think not!

  • As I understand it, the uk and Ireland are the only countries in Europe that use system boilers rather than combis. I can see why, installation is much simpler with a combi. Best of luck, get a plumber familiar with Tado and Opentherm and something may be possible.
  • GrilledCheese2
    GrilledCheese2 ✭✭✭
    edited September 2022

    @DFlinter Glow Worm is owned by Vaillant. The Smart Wiring Centre 2 is reportedly a rebadged Vaillant VR66, which is not compatible with Tado thermostats. The previous generation of the Smart Wiring Centre was a rebadged VR65 and some users on this forum reported it as compatible with Tado. However, this earlier generation was only capable of controlling two zones; CH & HW.

    If you want multiple zones with temperature modulation you'll probably have to switch to using Glow Worm's own controls.

  • Thanks @GrilledCheese2 & @johnnyp78

    Don't fancy changing from Tado so I guess I'll just wait until I get a new boiler in the future

    Out of curiosity, based on what I've described as my setup, is there any system boilers that are modulating, have Opentherm and can appropriately manage hw?

  • I think there are unlikely to be because the system boiler market is so small compared to combis, and the historic lack of interest in digital connections on boilers in this country, but I’m happy to be proven wrong.
  • Just had a look around, assuming I’m allowed to post links to other forums it looks like it can be done, but only with evohome
  • I take it back, looks like intergas boilers can do it