Boiler modulating control while keeping the thermostat relay output to turn on/off floor pump?


I currently have 6 wired thermostats controlling my underfloor heating installation. The thermostats switch their corresponding relay outputs, which are wired to the heating control panels on each floor of the house which, in addition to turn the boiler on / off, also control the start / stop of a floor circuit pump, which is totally independent from the boiler.

So far the system works perfectly with this on / off type control. The boiler is a Thermor Naema Micro 35, and I have just come to know it can perform modulating heating control with OpenTherm.

My question is whether, by acquiring the Extension Kit and connecting it to the boiler, I could carry out the modulating control of the boiler, instead of the current on / off control, but in such a way that the thermostats would continue to actuate their relay output so that they keep controlling the start / stop of the floor circulating pump, which as I said is independent from the boiler.

After having a look installers manual, it seems that for modulating control with OpenTherm the thermostats must be configured as option 'D01'. However, I understand that they should remain configured as 'R01' so they keep switching their volt-free relay to control the start / stop of the pump. But If so, I don't know whether they will send the signal to the Extension Kit to carry out the modulating control of the boiler.

Thank you very much in advance for your help

Best regards,



  • Montage
    Montage ✭✭

    You can use relay OR modulate in Tado land.

  • Antonio, what are you aiming to achieve from the boiler modulation? Is your floor circuit pump also accompanied by a manifold with its own thermostatic valve? Mine is and so it does not really matter what temperature the boiler is set to, the temperature to the floor will be that set by the manifold. Ideally this manifold valve could have some seasonal/Opentherm control but that is beyond Tado.

    Alternatively, is your boiler water sent directly into the floor circuit at whatever the boiler is set to? In which case I would be concerned that Tado, which is better suited to radiators, would set the boiler too hot with OpenTherm.

    I have been planning to have a play with Opentherm to see what can be done with my mixed radiator / UFH set up, but cannot help with the relay setting yet. Though I had though the smart thermostats might be able to stay at R01 and just change the extension kit to D01. But have not tried this yet.

    Also you say the system works perfectly with on/off? Floor heating is generally slow to respond, so do you get much overshoot with tado as I do?

  • Did anyone get a definitive answer to this? Or did you try it?

    I am trying to achieve the same thing. I would like to utilise the switched output but also control the boiler using the digital outputs.

    In my case I have the extension kit using the digital output for the boiler and a wireless stat. Would look to buy a second stat but want that one to be able to control a valve.
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