Is it possible to effectively use a tado extension kit to replace a three channel controller.

edited November 2019 in Technical Questions

I have underfloor heating downstairs and radiators upstairs. I also have a hot water storage tank upstairs. The timings associated with the firing of the boiler are managed by a three channel controller (Horstmann ChannelPlus H37).

I have installed tado smart thermostats in each room downstairs, set the 'downstairs' channel on my Horstmann controller to permanently on and these work well based on the schedules I have created in the tado app.

I have installed tado smart radiator thermostats upstairs on all the radiators. Again these work well with the schedules I have created in the tado app - HOWEVER - upon setting the 'upstairs' channel on my Horstmann controller to permanently on, in anticipation of the tado radiator thermostats managing the call for heating, the 'heating' actuator for the upstairs area immediately opens and starts the pump next to the boiler. This actuator remains open and the pump continues to circulate water from the boiler to the radiators irrespective of whether or not any of the tado radiator thermostats are calling for heat or not. While this 'theoretically' works, in that the radiators will only actually heat up according to the schedules I have created in the tado app, the heating pump remain permanently on. For example, during the night when I have set the tado radiator thermostats very low (13), the pump keeps on pumping all night.

It had been my intention to continue to control my hot water needs using the third channel on my Horstmann controller, however I have now also purchased a tado extension kit and would like to install this in the hope that I can configure it such that the heating pump only comes on when the radiators are actually calling for heat while it also controls my hot water demands.

Tado have indicated they do not have instructions to replace a three channel controller with an extension kit and have suggested I contact a local electrician to change the wiring.

Has anyone in the tado community successfully 're-wired' the actuators in their system such that a tado extension kit can replace a three channel controller.

Any advice/guidance greatly received.


  • Just by way of follow up ......

    I have now managed to accomplish what I was hoping to. 

    My tado Extension Kit is now in place and is actively controlling my upstairs radiators as well as my hot water supply. Both are operating effectively via the schedules I have set in the tado mobile phone app. In addition, the tado wall mounted smart thermostats are now effectively controlling my downstairs underfloor heating, again via schedules I have set up in the tado mobile app. Key to this however, is that the downstairs underfloor heating and the associated thermostats are not associated with the Extension Kit, but are operating independently of it, and I have simply directly wired (in behind the Extension Kit) the wires controlling this, which was the original channel one on my previous Horstmann three channel controller. My original channels two (upstairs heating) and three (hot water) are now wired in as channel one and two on the tado Extension Kit. The success of this is down to Tado support staff, who at my request, remotely configured the Extension Kit to ignore the downstairs thermostats, and to simply interact with the upstairs radiator thermostats (wirelessly) and the hot water system.

    Having set this up I did, for a number of days, have the ongoing problem that the downstairs actuator would not switch off even when no thermostat was calling for heat and as a consequence, the boiler pump and the downstairs underfloor heating pump, ran continually (24/7). I tried several re-wiring arrangements without success but then I temporarily disconnected all thermostats (seven downstairs and nine upstairs) and reconnected them all again and mysteriously everything now works exactly as it should. When the downstairs thermostats stop calling for heat, the actuator closes and the pump stops. At the same time I can, via the mobile phone app, have any or all (or none) of the upstairs radiators and or hot water, successfully calling for heat. 

    While it has taken me a few weeks (and some cursing) to work it all out, it is now working exactly as it should and exactly as I wanted it to, but of course with the significantly added convenience provided by the tado mobile phone app, allowing me to turn heating on/off to any room from literally anywhere in the world and indeed the additional benefits of the geofencing etc.

  • Hi Cor,

    Hoping you can help, I followed your posts and the situation sounds similar to mine. I have an existing 3 channel ESI programmer and Tado have just said to send everything I've purchased back as it's simply not compatible.

    What you've done sounds like it is though. The bit I'm not quite clear on is when you say "I have simply directly wired (in behind the Extension Kit) the wires controlling this, which was the original channel one on my previous Horstmann three channel controller."

    Does this mean you have an extension kit and thermostat controlling one zone and the hot water and then you've directly wired in a second thermostat to control the second zone? Or have you doubled-up the wiring for zones 1 and 2?

    thanks in advance.

  • Hi jdku2003,

    Before Tado I also had a ESI 3 Channel Programmer; Hot Water; CH 1 for ground floor and CH2 for 1st floor radiators. I also had thermostats in the hall on the ground floor and in the master bedroom for the 1st floor. The thermostats controlled the motorised valves for each floor.

    I now have the following setup; extension kit replacing the ESI programmer, controlling only the hot water. Two smart thermostats replacing the existing thermostats. 5 smart TRVs; 3 on the ground floor and two on the 1st floor. More smart TRVs to come later.

    I asked Tado Support to only allow the extension kit to control the hot water. Each smart thermostat was assigned a floor (zone) along with corresponding smart TRV. Tado support did say I would need an electrician to rewire but being an electrical engineer it was a no brainer to 'swap a wire' at the extension kit. Now the smart thermostats are independent of the extension kit.

    Now when a radiator calls for heat it will ask the smart thermostat assigned to that zone to switch on; which in turn activates the motorised valve for that zone causing the pump and boiler to start.

    I still have a 3 radiators that don't have smart TRVs, they heat up whenever the smart thermostat or a smart TRV calls for heat depending on the zone; 1 on the ground floor and 2 on the 1st floor.

    I hope this helps a little, don't give on Tado.

    Thanks, Sparky

  • Amazing, it sounds like the exact same setup!

    I'm not an electrician so it sounds like I'm going to need one as I don't know what to do with the CH1 and CH2 wires that are currently going into the ESI programmer. I guess they have to be terminated somehow? Wiring the thermostats is simple enough.

    I'll see if I can find a sparky! Thanks for your answer

  • No worries, the thing here is getting Tado support to setup the backend config; zones and smart TRVs. Before the smart TRVs were added I had CH1 and CH2 in the same connection on the Extension kit. On the back of Extension kit is schematic, it's essentially two relays, one for hot water and one for central heating. With two positions, Normaly Open and Normaly Closed. As long as Tado doesn't switch on my CH heating using the Extension kit my setup will continue to work via the smart Thermostats and TRVs.

    On a side note, I live in rental property so any changes I made are very easily reversed.

    Thanks , Sparky
  • Ah ok, I had wondered about putting both zones into one. I can do that simply enough. I've emailed Tado and asked them if they'll do the same for me as they've done for you, fingers crossed they will and not just give the usual answer of "take it all back", which seems a bizarre response.

  • Hi there jdku2003,

    Please accept my apologies. Since resolving my issue and posting above in Dec 2019, I have not revisited this discussion forum until today. Nor did I get any notification or email indicating anyone had commented or questioned my post.

    While it is probably far too late to be of any use to you, I am attaching a schematic diagram, showing how I moved the existing wiring of the Horstmann H37 Channel Plus, and wired those existing wires to the Tado Extension Kit.

    Please note - I am NOT an electrician and I am most certainly NOT advising you or anyone else to implement this solution. All I'll say is I did this in December 2019 and my system (all upstairs radiators, all downstairs underfloor heating and the hot water) has been working perfectly since.

    In the attached schematic (powerpoint) the top part represents the Horstmann and the way the existing wires were attached to it. The bottom part represents the Tado Extension Kit and the way I attached the existing wires to it.

    The 'directly wired' piece that you queried is effectively where multiple wires from the Hosrtmann setup are relocated to a single connector in the Tado setup. Note however, this only worked due to the remote re-configuring that Tado did for me (as described above).

    Hope this is helpful and sorry again for the delayed response.

  • hi @Sparky can you please share your wiring setup for extension kit as I also have ES3247B timer for heating and hotwater.

    From your above description I did get most of it but not 100% sure so some visual image would be nice.

    My understanding is

    • Connect Both zone wire to CH0 of extension kit and connect HW to CH1
    • then request tado support to always keep CH0 on! This way extension kit only control the HW

    is this right?

    can anyone help me with the setup please :( Tado support say they dont support this officially but unofficial its possible! I wish they would publish some guide for such setup with outlining limitation.

    also its been very common to have multiple zone i am surprised tado didn't manage to find official solution.

  • Hi @vjain419 have you replaced the room stats with the Smart Thermostats for each zone and are they wired? This setup only works with Smart Thermostats are Wired / 230v Relay.

    There are two issues:
    If you connect the heating zones to CH OFF (my current setup) and Tado don't make changes to the Extension Kit config when there is a call for heat in either zone, neither zone will heat.

    If you connect the heating zones to CH ON then only one zone will heat and other will only heat when both zones are asking for heat at the same time.

    From my experiences and looking at s-plan wiring diagrams the Central Heating side on the timer supplies power to the room stats, in theory if you connect both heating zones wires to the live at the Extension Kit rather than CH OFF, you shouldn't need Tado to make any changes to the Extension Kit config. The Smart Thermostats then become the controller for each zone as they should be. Depending on your wiring there may be insufficient space in the backplate, you might need looped terminal block.

    I suggest you setup the Internet Bridge, pair everything up then ask Tado to setup the multi room for the Smart Thermostats and the Hot Water. If you have TVRs, get Tado to assign them to the relevant Smart Thermostat zone.

    Photo of my Extension Kit >

    Hope this helps.

    Cheers, Sparky

    If in doubt, seek help from a qualified electrician.
  • Hi Sparky, any chance you could repost the photo of your extension kit? Many thanks
  • Hi Malck, as requested.

    Thanks, Sparky

    If in doubt, seek help from a qualified electrician.

  • Malck
    edited November 2020

    so sparky, this is the wiring I have. What do I need to do to CH1 AND CH2 with the extension kit to ensure they are permanently on for the stats? Thanks

  • Hi @Malck what is your current setup?

    Do you have TRVs?

    Have you replaced the room stats with Smart Thermostats?

    Are the Smart Thermostat in Heating Zones (Tado calls them Rooms)?

    Are the TRVs assigned to a Heating Zone?

    Thanks, Sparky

    If in doubt, seek help from a qualified electrician.

  • Malck
    edited November 2020
    I have an ‘S’ plan setup. Wired tado smart stat upstairs and downstairs and smart radiator trvs on each floor linked to the stat for calls for heat, so yes linked to each zone appropriately.
    I was thinking of linking it up as below
  • Malck
    edited November 2020
    Wiring live and neutral as normal. Then the 2 heating channels from the horstmann h37 channel plus (1,3) into terminal 4 of the extension kit or zone 1 to live and zone to 4. Then Finally wire the hw (5) from the horstmann into terminal 3 of the extension kit.

    I’m unsure if I then Need a bridging wire to connect terminal 4 to the live terminal of the extension kit. I guess that would give live feeds for both stats, which is essentially what I have at the moment as the programmer in zone 1 & 2 on the Horstmann are set to permanently on. The stats then calling for heat when needed. Thoughts?
  • Malck
    edited November 2020

    Like this (but not sure if I would still need a bridge from terminal 4 to live if doing it this way or if having both 1 & 3 into 4 on the kit with a bridge to live is better.)

  • Hi @Malck

    Wire the HW to 3 as normal. Bypass the Extension kit for the heating zones by connecting them to the Live, essentially this is the same as putting the 3 channel permanently on for the central heating.

    The Smart Thermostats become glorified relays, I have mine set to off in the app. If they call for heat without a TRV open then the pump could be damaged, more likely your system will have a pressure bypass valve fitted as a safety measure.

    When I wired both heating zones to 4 only one Smart Thermostat would switch on the Extension kit after a TRV called for heat. The other Smart Thermostat couldn't tell the Extension kit to switch the CH on. Tado support said the backend config wouldn't support this setup.

    Thanks, Sparky

    If in doubt, seek help from a qualified electrician and plumber.

  • Malck
    edited November 2020
    That’s great. I’ll do that. How do you switch the relays off in the app? Is it simple to do or was there a code I needed to select? I can see in the installers manual there are a number of codes you could select. Getting the kit on Thursday, so preparing for it. Thanks again.
    Also, out of interest, what do you have linked to no 2 on your kit?
  • Just set both Smart Thermostats to off in the Smart Schedule

    I have my heating zones connected to 2, it's the same as connecting to the Live as Tado support disabled the CH on my the Extension kit.

    Cheers, Sparky

    If in doubt, seek help from a qualified electrician and plumber.

  • Installed the extension kit as your described Sparky at the weekend. Both heating zones wired to perm live (using a terminal block for both zones then a single wire to perm live) and hot water to no 3 on the kit. Didn’t work at first as when you install the kit it thinks you have a wireless smart stat and only one heating zone. But got on to tado support and after many conversations they finally understood I only want the extension kit for hot water and that both stats are wired and just being used as relays. They needed to remap the radiator valves to each zone again (so it’s handy to have a note of the serial numbers of each valve and which stat they should link too. So prep for that) Got there eventually after almost a whole day of support chats. Note to others - Don’t install at the weekend as tado support is not available. Only available Monday to Friday at present.
  • cvt123
    edited December 2020

    Before my questions at the end, a bit of a preamble

    ere is my set up before installing Tado

    I have two zone heating and hot water

    a. CH1 - upstairs which used to be controlled by a wire thermo and has its own valve

    b. CH2 - kitchen underfloor heating which was controlled by a wireless thermostat.

    My plan WAS to use TRVs in the upstairs (about 12 radiators) and set up to two extension kits to manage each CH separately. Having bought everything and installed most of it, I have found out Tado does not support two extension kits on the same account (pretty silly, btw). But it seems that this thread may have found a work around...

    My original plan was to connected both CH to slot four (CH on) which means that they both work in tandem. My issue with this is that if the underfloor heating thermo tries turns the heating off while the TRVs turn the heating on, then the underfloor heating will continue as the valves will remain open. Not ideal. I then hooked in the wired thermostat (its an old dial system) between the extension and valves on CH2 to act as a manual switch. Pretty clunky.

    From the thread, it seems that one option is to connect CH1 to live in on the extension kit so it remains permanently on and then the TRVs will draw upon the heating whenever they switch on. Love the elegance but I am a bit hesitant because (a) not sure how I feel with the pump going on all the time and (b) some radiators dont have TRVs so there is some manual work. 


    The other idea I had would be to the existing wired thermostat with a Tado smart thermo and then link it between the valves of CH2 and the extension kit. I would add the second Smart Thermo to the kitchen and set it on 15 or some low number so it never gets activated by the temperature. In the kitchen, I would make the smart thermostat that is physically in the kitchen as the 'measuring device' in the settings. My hope is that when the temperature in the kitchen drops to trigger the smart thermo, this will then ALSO trigger the second thermo to complete the circuit to open the valves for CH2.

    Could this work?

  • cvt123
    edited December 2020

    (I duplicated this post, so deleted the second one. Unfortunately, i cant delete the post itself, so I have to write this)

  • Hey folks,

    Just wanted to say thanks for this thread! I'm in the same situation and have gotten so far as to bypass both heating zones and have the hot water being called for but boiler not firing yet :/ I'm hoping it's something tado support can sort tomorrow!

  • Sparky
    edited October 2021
    Hi @obistevekenobi does your system have a hot water interlock?

    Cheers, Sparky
  • Hey @Sparky - I have no idea to be honest. The setup was as follows:

    • oil fired heating
    • EPH 3 zone programmer (model t37)
    • 3 zones are hot water, ground floor heating (wired stat), first floor heating (wired stat)
    • There is also a back-boiled stove which provides heat to the ground floor as well as heats the hot water once it's on and hits a certain temperature

    An interesting aspect of getting this working was that in my starter kit I got a wireless thermostat (that I'm not using), but the v3 extension kit wouldn't even trigger the hot water relay until I paired the wireless stat :/

    If you have any thoughts on what I could do to fix this, they'd be greatly appreciated!

  • Oh, there is one of these labelled 'hot water' fixed to the stainless steel tank:

  • Hi @obistevekenobi
    I've looked at the t37 manual, I don't see interlocking. I think the hot water hasn't been enabled in your config.

    You mentioned that you have a wireless thermostat. This is used to program tado, basically tells the system that you have an extension kit and enables hot water in the Extension Kit. Google Smart Thermostat 230 V Relay Installations Guide for Professional Installers pdf.

    The device on your stainless steel tank is your tank stat, controls the hot water temperature. The only information that tado doesn't report.

    Cheers, Sparky
  • Thanks a million @Sparky

    I chatted with Tado support yesterday and they wouldn't do anything without a picture of the extension kit wiring (I'm not at the house for a few days) even though I explained the setup in detail :/ Hopefully it's simply a case of them enabling the hot water once I get down there next.

    I'll let ye know how I get on.

    Thanks again.

  • Hi, I'm trying to install the tado into my girlfriend's new build, where they have this 3 channel ESI programmer. I'm not using any TRVs, only 2 wired thermostats, and the extension kit

    1. If I took ch1 and ch2 off the esi and plugged it into the CH ON, on the extension kit, based on the schedule in the app, the CH ON would send a switched live to both wired thermostats

    2. The wired thermostats would then be able to control their own valves based on the temperature of the room, effectively still giving control of the 2 zones right?

    The assumption I've made here is that the programmer only sends a switched live to however many thermostats that are connected to the CH ON, and the thermostat then controls the valve which in turn controls the boiler and pump. The thermostat being a relay allows for there not to be a feedback loop causing both zones to fire if either call for heat.

    Assuming what I've said above is correct:

    1. Why would one of the heating zones not be working independently, I can get the downstairs zone to turn on as expected but the upstairs won't turn on.

    2. I get bridging the live into the CH ON but that seems unnecessary, since via the app you can provide a live to the CH ON, its just that the live will get sent to both wired thermostats, but the thermostats still retain independent control based on the room temp as all that's inside is a temperature controlled relay, and therefore each thermostat should be able to fire the boiler and pump?

    Thank you
  • Hmm seems to have decided to work as planned this morning.

    So ch1 and ch2 plugged into CH ON, wired thermostats both get a switched live via the app, so when one gets a live, so does the other, but the thermostats then control the valves