Opentherm with Ideal Logic 30 Boiler

Hi everyone, I’m hoping somebody here might be able to offer some insight on a technical question I discussed with Tado customer support today.

I’ve currently got a setup consisting of two smart room stats, numerous smart TRVs and an extension kit. The boiler is being enabled by on/off control from the extension kit. I wanted to know the benefits of using the opentherm connection instead so contact Tado support. They have informed me that despite my boiler having opentherm capabilities, I am unable to connect it to my extension kit in this way. To quote their response: “ I've just checked your boiler and unfortunately we can not control this boiler using Opentherm. We can only control it via simple relay (On/off). This used to be possible, but connection to this interface needs an extra harness, which is why this interface is disabled for our devices.”

Does anyone know anymore about this or why opentherm can’t be used on my specific boiler model?

Just as some background, I’m a building management systems engineer, and I understand the principles of weather compensation, etc (although I must admit I don’t know a lot about opentherm protocol!).


  • jelockwood
    jelockwood ✭✭✭
    edited February 2020


    I cannot say for certain what Tado's reason is but I can say that On/Off control aka 'Call for Heat' control uses different wiring to OpenTherm.

    OpenTherm is a digital interface and only needs two wires and also runs at a different voltage. Call for heat is 220v and uses switches aka relays to turn that connection off. Typically you have wires for power, for the heating pump, and the heating mid-position valve, along with wires from the room thermostat to indicate whether heat is required or not.

    It could be that Tado are implying that the cabling to your Boiler needs to be replaced, or cabling within the boiler to link to their OpenTherm system.

    A possibly related example is that some Vaillant boilers can be fitted with a timer/controller on the front of the boiler and wirelessly linked to a matching room thermostat. With this example Vaillant setup there is no external wiring at all and hence nothing to link the Tado to. Perhaps they are viewing your setup as being like that.

    Here are some links that might help you.

    The wiring loom apparently comes with the Weather Compensator kit.

    Note: You do not want to fit the Weather Compensator itself as it would conflict with Tado's own OpenTherm control of the boiler.

  • Did you ever get this working? I have replaced my Nest gen 2 with Tado specifically for Opentherm + smart TRV’s and I spent hours of trial and error with no success.

    So we weren’t with heating last night I just wired it up to the relay for the night but I can’t understand why opentherm just doesn’t seem to function. Surely the whole point of opentherm is that it uses a universal communication so it doesn’t matter what thermostats/boilers you have?

    Any help would be much appreciated! So far it feels like a bit of a let down and I expected the opposite
  • I should have noted that I too have an Ideal Logic Combi 35
  • I've set up Tado with an Ideal Logic Combi 35 using Opentherm.

    For my boiler (part 47-348-58) it needed a wiring harness which came with the weather compensation kit (part 204914). A two wire plug connects to the PCB for the weather compensation part and then the Opentherm plug connects to the harness.

    Once the Tado low voltage digital outputs were connected it was just a case of making sure Tado was in Opentherm mode (D01 -> HC01).

  • Appreciate your feedback NeonDusk! That’s exactly how I had mine set yet it fails to work properly. This is the harness I needed so wonder if our control boards differ?
  • NeonDusk
    edited October 2020

    Apologies if this is an obvious question but did you connect you connect the two Opentherm plugs together? I've labelled them in the picture below.

    The other thing I would suggest that if the cable to the Tado thermostat is long you could temporary move the Tado closer to the boiler and try a different shorter cable.

  • you don't need the harness, just put the wires into the choccy block and tighten. If you search for logic combi opentherm kit it shows a better diagram for pulling the spare socket out of the empty timer box and reattaching etc. Not difficult.


  • NeonDusk
    edited December 2020

    Some of the Idea Logic boilers do need a harness as they have nothing connected to the Opentherm port on the PCB. My Logic Combi 35 needed the harness below which comes with the weather compensation kit.

    And this is it connected using Opentherm

  • Hello, I have an ideal logic 30w and already use tado connected on/off just.
    @NeonDusk what benefits have you noticed with using this setup? I take it it uses tados weather compensation. I've noticed that the boiler is nearly too powerful for my house now as only half the rads are on at a time really. Does the ideal modulate to compensate for this? The rads are so noisy when only three or four are on at night. Wakes the wife up. Not me- I sleep through anything.
  • I need some help with my Ideal Logic 30 setup. I got the same answer from Tado that Opentherm mode is not supported but with the positive comments here I'm confident it can work.

    @MrB @Arki did you manage to get this working?

    @NeonDusk did you enable Opentherm yourself using the Smart Thermostat? I don't think I am able to do this myself using the Extention Kit.

  • You can switch it over to OpenTherm yourself.

    See the professional installer manual at for how you can set it to OpenThem (D01) instead of Relay (R01)

  • tadouser1000
    edited February 11
    @NeonDusk the instructions show you how to enable with a Smart Thermostat but I've only got an Extension Kit with Smart TRVs. Was hoping you had a similar set up but it seems like you've got a Smart Thermostat which let's you enable Opentherm yourself

    Thanks for getting back to me so soon :)
  • I see, thought you had an extension kit with wireless thermostat.

    In your case I think it would need Tado support to switch it to OpenTherm.

  • So just to update, I got support to enable Opentherm for me so I've got it all working now. My Ideal Logic 30 did not require a harness so it's possible that newer models don't require a harness for Opentherm.

    Just to note, support told me if I select Ideal Logic + model this would trigger an Opentherm installation. I did not try this so cannot confirm that this would work.
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