Junkers TRQ 21 T Thermostat

I have a Junkers TRQ 21 T Thermostat in my flat and it has two disadvantages.

  • there is an old timer clock that ticks every second which is annoying if you are not used to it (like my guests) :loudspeaker:
  • you only control specific time slots to switch between day and night mode. No differentiation between work days and weekends. :disappointed:

So I developed a controller, to connect an arduino (Wemos D1 mini) to be able to control my thermostat with openhab.

You can find my documentation here:

Hi Christoph,

I have the same thermostat. Perfect to find such a solution. If I understand your approach right, you are using the clock input to control the thermostat. I found out that the thermostat controls the boiler temperature by modulating 0-24V if I remember right. At the end of summer I will give it a try. Thank you to share your informations. I come back to you with a feedback … or questions:-). I am no programmer so I hope I can follow your instructions.

I wish you a nice weekend!

Nice to hear my solution will be useful for other people as well. :slight_smile:

Unfortunately I finished this project exactly when the β€œsummer” started.
So I have no real life experience, yet. :smile:

At first I thought I could use the 24V modulation as well.
But I read somewhere that the thermostat does a little more than just setting the boiler to ON or OFF.
So replacing just the clock seems to be the safest solution.

Hey Christoph,

I have not the same but a similar thermostat. TRQ 21 (I think its just an older version.)
Did you already get some real life experience?

I think i will try to adapt your solution to my thermostat in the nearer future.

Yes, I had no problems in the last weeks. :grinning:

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Hi, I have also spent alot time thinking about how to control my Junkers Heating a bit more smart. I also planed to build an Arduino based controller on my own to completely replace the existing room controller (TR100 in my case). But last year I found the Tado Smart Thermostat as replacement for the TR100 which covers all my needs out of the box.

  • Perfectly compatible to almost all Junkers Heating especially the ones which can be controlled by a TRQ21 or TR100
  • Individual Heating Plan for every day
  • Automatically Switch to Away mode by GPS Location of the Smartphone
  • Manual control
  • Early Start (start heating when I come clother to my home)
  • Perfectly integrates with Homekit, Alexa, IFTT and openHAB
  • a nice smartphone APP to configure everthing and see stistics
  • Not too expensive
  • Works out of the box without the trail and error a self build themostate would bring until it works as expected.

Especially because of the presencedetection in combination with the Smartphone app I use a very simple heating timpleplan. Only day and night, all other things like work, holidays etc works automatically.

There are also Tado Radiator Thermostats but for this I use the much cheaper MAX ones controlled by homegear. OpenHAB Switches the MAX thermostates to ECO mode if the Tado Thermostat is in Away Mode.

Tado might be a good alternative.

But I do not think it is cheap.
When I first heard about tado, they were only renting their devices (I think), which was a no go for me.

You can implement almost all features via openHAB.
Use OwnTracks for location tracking.

But working out of the box is a great feature, of cause.

The heating system in my house was replaced and my Junkers gas boiler is no more.

Now I have no need for my custom controller anymore.

If somebody is interested I would send it for 10 € + shipping in Germany. (no guarantees)

Hi Christoph,
i’d be interested in your controller. I have a TRQ 21 and it doesnt suit my needs either.
Although i am quite new to this, heat controlling, smart home, openhab, i think this could help. Is it still available?
Thank you!