Junkers/Bosch Cerapur 2200 configuration


Does anyone have simillar problem with Tado wireless thermostat V3+ and Junkers Cerapur 2200?

The receiver is connected to the heater in accordance with the instructions. It receives a signal from the wireless controller and radiator heads and the fourth LED starts flashing = transmits the signal to the heater. I checked both HT-BUS (D17) and EMS-Bus (D31). The heater does not start.

Junkers heater works properly because after permanently shorting the relay input, it heats all the time. The option to use relay input after connecting the COM and NO contacts and resetting the control unit (default relay mode) also does not work.

Please advice.


  • This might be something you already know, but have you checked that Tado is compatible with your boiler’s ebus protocol?
  • LukasT
    edited October 2023

    I checked with Bosch - they promote their EMS-BUS which is supported by tado. Cerapur manual clearly shows 2 wire bus communication port available. There is also standard potential free 2 pin connector that works with a piece of wire. Unfortunatelly when I reset receiver it is not closing relay output (COM+NO) while receving heating commends from the bridge (thermostats) confirmed by 4th led pulsating.


    This boiler speaks a language called EMS2 BUS. tado° doesn't speak that language yet, therefore it can't communicate with the boiler.

    To resolve this, please follow the instructions for the boiler, in your tado° app. The boiler will have to be wired in Relay on/off mode.

    You can find customised step-by-step instructions in the tado° app, to help you install your tado° devices quickly and easily.

    By following these steps, tado° will also automatically configure itself to your specific heating setup. This means that you won’t need to change any settings via the Installer Menu on your device.

    Here’s what you need to do to proceed:

    1. Create or sign in to your tado° account.
    2. Add your tado° devices to your home. If this is not your first installation, you’ll need to go to Settings > Rooms & Devices and select Add Device.
    3. If you’ve already added your devices, select the tado° device you’d like to install.
    4. Then, select Installation Instructions.
    5. Next, select the make and model name of your boiler -> The name is Bosch Condens 2200 W
    6. Follow the installation instructions for your tado° device.


  • Is it possible to use 7746901847 convertor to OT and use Open Therm with Tado?

    It it very bad that Tado doesn't fully support EMS even if it claims that in the installation guide.
  • I'm successfully using a 7746901847 convertor on my Cerapur Acu 22/28. I switched from Nest thermostat (3rd Gen) to Tado last month. It's working well for the heating. Two things are weird though: 1) if the heating boiler ran for a while, the boiler does not deliver more heated water even though a tado radiator valve is requesting more, eventually it resumes, I guess that's a limitation by the boiler, and 2) the hot water control seems to be always on, despite what's configured in the schedule.

    But I'm overall happy with the switch, but I've only just started with tado, so I can't say if it actually saves me money over the Nest.