How to connect Stiebel Eltron heat pump (EVU contact via Shelly) with Reduxi controller
Connect the EVU contact of your Stiebel Eltron heat pump to the Reduxi Controller via a Shelly.
1 Technical documentation
Manufacturer documents for the heat pump:
- Stiebel Eltron: Technical guide WPL 15/20/25, engineering and installation – Planning and installation document for the WPL 15/20/25 air-to-water heat pumps (PDF).
- Worcester Bosch: literature search for HPC410 – Link from the original article.
2 Required equipment
- Reduxi Controller
- Stiebel Eltron heat pump with an EVU contact
- Shelly with an input contact (I) and an output contact (O)
- Wire to connect the Shelly to the EVU contact
- Laptop or tablet with internet access to configure the device in Reduxi
3 Connect the EVU contact to the Shelly
The Reduxi Controller uses the EVU contact of the heat pump for Smart Grid support. A Shelly switches the contact.
3.1 Find the EVU contact on the heat pump
The picture shows an example of the terminals of the heat pump. The terminal L' is the EVU contact.
Text description of this image
Photo of a heat pump terminal strip diagram (Stiebel Eltron), photographed at an angle, with Slovenian labels written vertically above the terminals. Left: a blue terminal block labelled N with five screw terminals and an earth symbol. Terminal labels in the coloured row, left to right, with the text above each: L (Napajanje [power supply], red); L (Napajanje [power supply], red); ON (Kompresor [compressor], green); KS (Črpalka - SOL [pump - SOL], black); KU (Hlajenje [cooling], light blue); MK (Črpalka - 2. krog [pump - 2nd circuit], red); L' (Napajanje L' - EVU [power supply L' - EVU], red); MA (Mrešalni ventil + [mixing valve +], blue); MZ (Mrešalni ventil - [mixing valve -], blue); HK (Črpalka - 1. krog [pump - 1st circuit], red); UP (Črpalka - TSV [pump - DHW], orange); WW (Signal - TSV [signal - DHW], orange). Red lines run from the L terminals down, the two L terminals are joined with a red dot, and L' is joined to the same red line; a black bar connects MA and MZ. A blue dashed line runs along the bottom. Further right: an earth symbol above a four-terminal block and a GND block with five terminals, then label X26 and terminals B1, B1 (red, labelled Predtok [flow]) and B2 (purple, labelled Povratek [return], partly cut off). Right and bottom parts of the image are white.
3.2 Connect the EVU contact to the Shelly
Take the wire from the EVU contact and connect it to the Shelly I (input) contact. This wire comes from the L power supply on the Stiebel Eltron.
From the O (output) contact on the Shelly, take a wire to the EVU contact L' on the Stiebel Eltron heat pump.
Text description of this image
Photo-based wiring illustration. Left: a white Shelly relay module (side view) with a row of six round screw terminals on top and a green LED on the front. Right: photo of the inside of a heat pump terminal area with white plastic panels labelled 400V 50Hz, WP, X3, N, X4, X24 (earth symbol), X26 and GND, a blue terminal strip near the top, a grey multi-row spring terminal block in the middle, a green-yellow terminal strip and a blue terminal strip lower down, and many wires in blue, brown, yellow and green-yellow. Two light blue lines connect the two right-most Shelly terminals to two terminals on the grey terminal block: the upper line goes to a terminal near the top of the block, the lower line goes to a terminal about five rows lower. A red X is drawn on the left side of the grey terminal block, next to the brown wires, marking a spot not to be used. Small labels HKP, UP and WW are visible at the bottom of the grey block.
3.3 Configure the Shelly user interface
Press the button in the Shelly user interface to switch the I/O switch on or off. Check whether the EVU is active when the contact is normally closed or normally open.
Stiebel Eltron sets this contact to closed by default, so that the heating keeps operating. If the contact is opened, the EVU contact is activated. The contact is therefore normally closed. Set this accordingly in the Shelly 3EM.
4 Log in to the Reduxi web interface
You can open the Reduxi web interface in two ways:
Text description of this image
Screenshot of three Reduxi mobile app screens side by side, with cyan boxes and number badges 2 to 4. Left screen (dashboard, dark theme): menu icon at top left marked with a box and badge 2; 'reduxi' logo; tabs 'Real time data' (active) and 'Statistics'; price 5.79 € and temperature 3.2 °C; energy flow diagram with a house in the centre (-1.25 kW) and icons with values 69.0 W, 1.3 kW, 1.1 kW (red ring), -165.0 W with 97 % (red ring) and 0.0 W values at the bottom; tabs 'Power' and 'Energy'; bottom navigation: Dashboard, Diagnostics, Device control, Settings. Middle screen (side menu): 'reduxi' logo, 'Number of locations: 1233', heading 'Reduxi device management', entries '+ Add Reduxi location' and 'Reduxi devices' (marked with a box and badge 3), then 'My profile' and 'About app'. Right screen (device page): Back; picture of a black Reduxi controller with two Ethernet ports; status 'Connected'; card 'Update available': 'New update is available for your Reduxi device.' with button 'Download and install update'; card 'Connect to configurator': 'Tunnel connection enables remote access to your Reduxi configurator, without need to be connected to the same local network.' with button 'Activate tunnel connection' (marked with a box and badge 4); card 'Unit details' with field 'Unit ID'.
Text description of this image
Screenshot made of two parts side by side. Left part: Reduxi mobile app screen on a dark background. Top: Back button; picture of a black Reduxi controller with two Ethernet ports and a terminal block; status 'Connected' with a Wi-Fi icon. Card 'Update available': 'New update is available for your Reduxi device.' with button 'Download and install update'. Card 'Connect to configurator' with a key icon: 'Tunnel connection enables remote access to your Reduxi configurator, without need to be connected to the same local network.' and button 'Open configurator', marked with a cyan box and number badge 5. Below: card 'Unit details' with a field 'Unit ID' (value not visible). Right part: Reduxi Configurator opened in a browser, marked with a cyan frame and number badge 6. Header: back arrow, 'Tunnel connection', reload icon. Left sidebar with icons (lightning, chip, lightning bolt, bar chart, gear). Page 'Home' with a green link icon. Green notice: 'New patch available. Click here to apply.' with a close X. Time 09:12:56. Energy flow diagram with a house in the centre (1.700 kW) and icons for grid (0.000 kW), solar (1.700 kW), battery (green, 0.000 kW and 0.800 kW), a device at left (0.900 kW), electric vehicle and a charger or device at bottom. Label 'Energy manager' at the bottom.
http://reduxi.local. You can find the controller's IP address in your router's device list or in the Reduxi app under Reduxi devices.admin · Password: admin (factory default)Text description of this image
Screenshot of the Reduxi Configurator login page in a Chrome browser window. The address bar shows 'Not secure' and 'reduxi.local'; the address bar is marked with a cyan box and an enlarged copy of it (cyan box, text 'Not secure reduxi.local') is shown at the left, connected by a cyan line. Page background: light grey line drawing of a house with solar panels (green), a wall box, an inverter, a car and a charger. Top left: 'reduxi configurator' logo. Login box in the centre with title 'Login', a language selector (English flag, 'English'), a username field and a password field, and a dark 'Login' button.
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Screenshot of the Reduxi Configurator web interface after login, light theme. Top left: 'reduxi configurator' logo. Header bar: 'Home' at left, green 'Connected' status at top right. Left sidebar: expanded section 'Devices' with a list of entries, then collapsed sections 'Manager' and 'Configuration' and 'Settings'. Main area: energy flow diagram. House in the centre with ring, value 24.20 kW. Grid icon at top left, 24.20 kW (red dot on its line). Solar icon at top right, value '-'. Left icon (battery or device), 6.700 kW (green dot on its line). Right icons (battery storage and a device), values '-'. EV charger icon at bottom left, 31.00 kW. A further device icon at bottom right. Label 'Energy manager' below the house.
5 Add the device to Reduxi
Use these steps to add a new device or to edit an existing one.
5.1 Basic settings
Log in locally to the Reduxi Configurator on the controller (see Point 4) and click + Add device. Then enter the basic settings.
5.2 Communication settings
Select the communication channel. Then enter the device configuration.
| Parameter | Value |
|---|---|
| Modbus unit ID | Normally one unit ID is used. |
5.3 Advanced settings
Enter and choose the advanced settings.
5.4 Test communication
Click Test communication at the bottom of the wizard. It reads the the device once and saves nothing. If the test succeeds, click Done: only Done creates the device.
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Screenshot of the bottom button bar of a Reduxi Configurator page. Left: button 'Back'. Right: button 'Test communication' (marked with a cyan box) and dark button 'Done'.
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Screenshot of the Reduxi Configurator page 'Communication channel and device configuration'. Connection *: TCP/IP (dropdown). IP *: 192.168.50.243, with button 'Scan for IP'. Port *: 502, with button 'Test port'. Modbus unit ID *: 1. Buttons at the bottom: Back (left), Test communication and Done (right). The Done button is marked with a cyan box.
6 Check the readings and set the strategy
6.1 Last measurements
After communication is established, check the values of the device under Devices in the Reduxi Configurator as an additional test.
6.2 Configure the strategy
Add an ON/OFF strategy in the Reduxi Controller. Define when the EVU contact is open. For example, you can set it to open when the limit on the grid meter is reached.
For details on strategies, see Strategies for Reduxi controller.
✓ Summary
Preparation (Points 1–2): Open the manufacturer document and gather the Reduxi Controller, the Shelly, the wire and a laptop.
Heat pump (Point 3): Find the EVU contact L', connect it to the Shelly I and O contacts and set the contact to normally closed.
Add to Reduxi (Points 4–5): Log in to the Reduxi Configurator, add the device and run Test communication.
Go live (Point 6): Check the readings and add the ON/OFF strategy that opens the EVU contact.
→ Common issues
| Issue | Solution |
|---|---|
| The EVU contact does not react | Check the wiring: Shelly I to the L supply, Shelly O to the EVU contact L'. Check that the contact is set to normally closed in the Shelly (Point 3.3). |
| The heat pump is not controlled | Check that an ON/OFF strategy exists and that it defines when the EVU contact is open (Point 6.2). |
| Open configurator does not open or stays empty | The tunnel is not active yet. Wait about 30 seconds and check that the controller is online. |
Login with admin is rejected |
The password was changed during installation. Ask the installer. The Reduxi account password does not work here. |
reduxi.local does not load |
Your device is not in the same network as the controller. Use the IP address or the tunnel connection. |
| Communication test fails, device shows offline | Check reachability, IP address / port / unit ID, and that the protocol is enabled on the device. |