Stiebel Eltron WWK-I

mampfes · June 7, 2025, 2:25pm

For 3 weeks now I own a Stiebel Eltron WWK-I 300 W Plus and I wanted to share some experiences (and questions ).

The WWK-I is a domestic hot water heat pump with 291 liter nominal content and an extra heat exchanger which I current don’t use. The WWK-I has built-in WiFi interface which is used to send a lot of data to the MyStiebel cloud. The device can be controlled via the MyStiebel app. There is no Home Assistant integration available, therefore I use classic means to integrate the pump in Home Assistant:

I measure the water temperature in the upper quarter of the boiler through a hole using a PT1000 temperature sensor:

Power consumption of the pump is measured with a Shelly PM Mini Gen.3 (12,55 € at Hornbach/Germany). The pump has 2 binary inputs to select between 4 operating modes:

Normal
Standby
SG Ready State 3
SG Ready State 4

SG Ready State 3 and 4 can be configured individually in the smart phone app. For each state, you can set:

Heating mode: Efficient (pump only), Balanced (optionally uses the built-in heating rod), Quick (pump + heating rod)
Target temperature, up to 65°C
Charge level (in German: “Aufladung”), which is a percentage value between 30% and 100%.

I use a cheap 2 channel relais module from Aliexpress which I reflashed with ESPHome to get rid of any Chinese software to control the 2 binary inputs.

Both modules fit easily under the removable front cover. The Shelly is the device on the right, the 2 channel relais module is the one on the left side.

This is an example of a pumping cycle. Ambient temperature is around 18°C. The pump takes 3:30 hours to charge the temperature from 42°C to 53°C (measured with my own temperature sensor). The configured target temperature is 55°C.

Together that is 1,65 kWh, using less than 500W.

So far I’m quite happy with the device and also the integration into Home Assistant. But ideally, I want to have all the values that are available in the MyStiebel app also in HA. And I’m annoyed that I have to use their app and that they don’t even have a browser based access to the MyStiebel cloud. Therefore I’m looking for other ways to get the data. Does anyone know if there is a local API available? If not, is there a way to grab the data from the MyStiebel cloud? Please let me know if you have insights.

mgguinne · June 19, 2025, 2:02am

Any luck with this, I am about to install one of these myself?

sanderkwantes · June 29, 2025, 10:58pm

Ha how funny, I also started the route to utilize the SG-Ready inputs, I did this with a Shelly 2PM.
I also spent some time reverse engineering the MyStiebel app. I have since developed a working integration for it as well. Feel free to start testing, I’d love to hear feedback. You can find the integration at: GitHub - sanderkwantes/mystiebel: A Home Assistant integration to monitor and control Stiebel Eltron devices via the MyStiebel cloud service.

mampfes · July 4, 2025, 8:58am

Wow, great - thanks for the work. I assume it was a huge amount of effort.
For my WWK-I 300 W Plus it works out of the box:

I just installed it, I will let you know if I have any observations.

hassioguy · September 26, 2025, 12:28pm

Hi, I’m interested in installing that model as well. Do I get it right, with the 2 Ch Relais you can force the pump to use the electrical heater (e.g. if there’s a lot of electricity from the PV on the roof) to optimise?

At you don’t need and extra device to connect the heat pump to the Wi-Fi? I saw that there is an ISP web from Stiebel. You don’t need that?

mampfes · October 5, 2025, 7:54am

With the 2ch relay you can enable the SG Ready States 3 and 4. What shall happen in these states can be configured in the app. For example, you can configure state 4 to heating mode “Quick”. Then the pump will use the electrical in addition to the pump. But you can’t (to my knowledge) switch on the electrical heater on its own.
And yes, with this setup, you don’t need to connect the pump to WiFi. And you don’t need an extra ISP.