Using the Nest thermostat with a modulating Junkers boiler (part 1)

Using the Nest thermostat with a modulating Junkers boiler (part 1)

In this blogpost I will tell you my story of how I wanted to integrate my central heating, with a smart home solution. It's a 2 part story, where I first go into detail about my setup before the nest. And the second part will be about installing the Nest.

Disclaimer: If you decide to do an installation yourself, be careful, there are risks involved, you might break your boiler, your Nest, or both, if you don't hook up everything correctly. I take no responsibility, consult a professional if you're not comfortable doing the installation yourself.

The Boiler


In 2014 we were in the need for a new boiler, as the one broke that came with the house we bought. I contacted our plumber and he got to work. I asked him about the Nest thermostat I learned about, but he told me that the Nest wasn't suited, because (at the time) Nest didn't support modulating boilers and using a Nest would mean my boiler would be energy inefficient.
He recommended an Junkers CerapurComfort ZWBR 30-3 boiler. For reasons he knew best, and I trusted him.

Junkers CerapurComfort

At the time there was a promotion, and with the purchase of a boiler we got a Junkers MB-LAN 2 Module for free (normal price was €300). Which would give us the ability to control our thermostat from an app.

Junkers MB-Lan 2 Module

The boiler came with the Junkers FR-120 modulating thermostat, which worked together with the Lan Module

Junkers FR-120 modulating thermostat

Review of Junkers material

We used this setup for nearly 3 years. And this is what I concluded.

The Boiler, and the thermostat worked fine, they did their job and were reliable.


For a device that would normally cost around €300, it is not worth it at all. The module requires a cabled connection to the internet, I managed to do that, but I can imagine others having their boiler in an unreachable place from the internet router.

If the internet went down, even if it was for a few seconds, the module would stop working, the only thing that you could to was unplug the power, and plug it back in, for it to completely reboot.
This was very frustrating for when you wanted to remotely turn on the heating before getting home, only to find out the module stopped working.

And it's not like I have a shoddy internet connection at home. With a coax cabled 100mbps down/10mbps up, very reliable network, I almost never have any complaints. (and I run multiple other devices reliably for my smart home, a Philips Hue bridge, a Rasberry Pi with Home-Assistant, and a Google Home).

Another frustrating thing was, that the regular thermostat gave a warning that there was a lan module connected, and every time I wanted to do something manual from the thermostat, I had to dismiss the warning ... every ... time ... I ... did .. something 😤.

The JunkersHome-App

If you want to use the Lan-module, you have to do it via the JunkersHome app. Which (at the time) costs €7 to install from Google Play

The app is just plain bad, not intuitive, slow as hell, and of course, stopped working when the Lan Module was unresponsive.

Trying to configure a schedule for the boiler via the app, is to date, the worst app experience I have had. The app would overwrite days I had already configured. Not save things I had put in, and sometimes take minutes to save.

External integrations

Lol what?

Of course nothing officially about this, only a handful obscure German forum posts from people trying to reverse engineer the Junkers/Bosch protocol, to read out values with their raspberry pi.

I also tried sniffing my local network to intercept the TCP/IP packages with Wireshark, so I could potentially write an application that simulated the JunkersHome app.
The packages, and URL endpoints led me to the forums, where some dutchies seamed to have did something similar with Nefit boilers. (this was my first indication that Nefit and Junkers arent all that different)

Nest Thermostat generation 3

The third generation of the Nest thermostat was released, and after reading the specs, I was delighted to find out that Nest was able to support Modulating boilers. However my euphoria was short lived, because even though Nest supported the OpenTherm protocol, of course my boiler didn't.

Junkers solutions

I talked to my plumber, and Junkers support about possible solutions. And I was recommended the new Junkers CT-100 smart-thermostat.

Junkers CT-100

€300 for a new thermostat, where I don't find that much about online, no integrations, no reviews, and my experience with their software from the Lan Module... no sir, I wasn't buying it (literally)

It was when I was researching this thermostat, I found the Nefit Easy, the Worcester Wave, the TC100 from Buderus and the Bosch Smart Room Thermostat. Fuelling my suspicion that these brands aren't all that different, all Bosch companies, with another name in different countries.

To give Bosch credit, the Nefit Easy seemed to have an IFTTT integration, but did that work with the CT-100? Nobody knows, no documentation about that anywhere.

In the next part I will go into detail of how I got the Nest thermostat working with my modulating boiler.


Read my follow up blogpost, on how to connect the Nest

Read Part 2