The Viessmann Vitogate 300 (Type BN/MB) is a gateway that bridges the Viessmann LON bus to Modbus RTU or Modbus TCP, enabling TapHome to control Vitotronic boiler controllers. This template is configured for the Vitotronic 200 HK3B and exposes 33 devices covering 3 heating circuits (A1M1, M2, M3), domestic hot water (DHW), and solar thermal monitoring.

The Vitogate 300 is a compact DIN rail module (100 x 48 x 70 mm) with RS-485, LAN (RJ45), LON (2x RJ45), and USB ports. It connects to the Vitotronic controller via LON and translates selected data points into Modbus registers accessible by TapHome.

Dynamic register assignment – The Vitogate 300 assigns Modbus register numbers dynamically based on which LON data points are selected in the web interface. The register numbers in the TapHome template correspond to a specific data point selection. If you change the data point selection in the Vitogate web interface, the register numbers will shift and the template will read incorrect values.

Hardware connection

Connection diagram

Front panel connections (left to right):

• Power LED – illuminates green when power is on
• Status LED – multi-color (red, green, orange) for operational status
• RX / TX LEDs – flash yellow during data receive/transmit
• DIP switch (A) – 1: Bias voltage RS-485, 2: Bias voltage RS-485, 3: 120 ohm terminator
• RS-485 (B) – removable plug with terminals: Shld, AGND, A- (Data-), B+ (Data+)
• PWR (C) – 24 VDC power supply connection
• LAN (D) – RJ45 for Modbus TCP/IP or web interface access
• LON (E) – 2x RJ45, screened, for LON connection to Vitotronic
• USB (F) – for firmware updates
• Reset – reset button

Technical specifications

• Dimensions: 100 x 48 x 70 mm (DIN rail mount, TS35)
• Power supply: 12-24 V AC/DC, max 320 mA (3.85 W)
• Operating temperature: 0°C to +45°C
• Protocol: Modbus RTU (RS-485) or Modbus TCP/IP (LAN port 502)
• RS-485 settings: 9600 baud, 8 data bits, no parity, 1 stop bit

RS-485 wiring

Connect using a 4-wire RS-485 connection to the removable RS-485 plug (B):

• B+ (Data+) –> A+/D+ on TapHome RS-485
• A- (Data-) –> B-/D- on TapHome RS-485
• AGND –> GND on TapHome
• Shld –> Shield (optional, for long cable runs)

RS-485 termination – DIP switch 3 enables a 120 ohm termination resistor. Enable it only if the Vitogate 300 is the last device on the RS-485 bus. TapHome Core has a built-in 120 ohm resistor on its BUS terminals.

Wiring in junction box

The Vitogate 300 and its power supply unit mount on a DIN rail inside the boiler junction box. The RS-485 connection (C) routes to TapHome. Power is supplied via 24 VDC from the included power supply unit.

LON connection

The Vitogate 300 connects to the Vitotronic controller via LON (RJ45). The Viessmann LON uses a “Line” bus topology with terminal end resistors at both ends. Use 2-core screened CAT5 cable or JY(St)Y 2x2x0.8 mm telephone cable. Maximum distance: 900 m with on-site cabling.

The LON communication module must be installed into the Vitotronic control unit. Depending on the controller model, this may be an additional accessory. Refer to the Vitotronic Installation and Service Instructions.

Configuration

Web interface access

1. Connect a PC/laptop to the Vitogate 300 LAN port with an Ethernet cable
2. Set your computer IP to 169.254.0.20 (subnet mask 255.255.0.0)
3. Open a browser and navigate to http://169.254.0.1
4. Log in with user name vitogate and password viessmann

Beginning second half of 2024, new Vitogate 300 units ship with a unique password printed on the device label. After a factory reset, the password reverts to “viessmann”.

Switching to Modbus mode

1. Go to General > Vitogate in the web interface
2. Set “Vitogate type” to “Vitogate 300 MB (Modbus)”
3. Set “Language of datapoints” to English and “Units” to SI units
4. Press Save, then go to General > Restart and press Restart

LON participant scan

1. Go to VI LON > Scan participants
2. Set System number: 1 and participant number range (e.g., 1 to 10)
3. Press Start – the gateway scans for Vitotronic controllers on the LON bus
4. After scan completes, check the desired participants and press Save
5. Go to General > Restart and press Restart (do not select “complete system restart”)

Data point selection

1. Under VI LON > Participants, click on a participant (e.g., 1.1)
2. Select the data point tabs (All, General, Boiler, Heating circuit A1, DHW, etc.)
3. Check the desired data points for transfer to Modbus
4. Press Save

Critical step – The data points selected here determine the Modbus register assignments. You must select exactly the same data points that the TapHome template expects, in the same order. Changing the selection will shift all register numbers.

Modbus configuration

1. Go to Modbus > Configuration
2. Set the Slave address (must match the Slave ID in TapHome)
3. For RS-485 connection, verify: Protocol RTU, Baudrate 9600, Databits 8, Parity none, Stopbits 1
4. For TCP/IP connection, the default port is 502
5. Press Save

The Modbus > Objects page shows the dynamically assigned register map with columns: Type (CO/HO/IN/ST), Register number, Name, Unit, and Format.

Status LED indicators

Device capabilities

Temperature monitoring

The template provides temperature sensors for all heating circuits and the solar system, reading from analog input registers with automatic /10 conversion:

• Outdoor Temperature (A:13) – damped outdoor temperature from the Vitotronic controller
• Supply Temperature A1M1 (A:27) – flow temperature of heating circuit A1M1
• Supply Temperature A1M1 Weather-Compensated (A:28) – weather-compensated supply setpoint for A1M1
• Supply Temperature M2 (A:60) – flow temperature of heating circuit M2
• Supply Temperature M3 (A:91) – flow temperature of heating circuit M3
• Solar Collector Temperature (A:150) – solar collector panel temperature
• Solar Storage Temperature (A:151) – solar buffer storage temperature

Heating circuit control

Each of the 3 heating circuits (A1M1, M2, M3) has independent operating mode and thermostat control:

Operating Modes (H:14 for A1M1, H:15 for M2, H:15 for M3):

• 0 = Off
• 1 = DHW Only
• 2 = Heating + DHW
• 3 = Continuous Reduced
• 4 = Continuous Normal

Current Operating Mode shows the active status (Off, Reduced, Normal, Continuous Normal) as a read-only indicator.

Thermostats provide room temperature control with current temperature reading and writable setpoint:

• Thermostat A1M1 Normal – reads A:22 (current), writes H:8 (setpoint, 10-30°C)
• Thermostat A1M1 Reduced – reads A:22 (current), writes H:11 (reduced setpoint)
• Thermostat M2 – reads A:62 (current), writes H:156 (setpoint)
• Thermostat M3 – reads A:93 (current), writes H:157 (setpoint)

DHW and room setpoints

• DHW Setpoint Temperature (H:1) – read-only domestic hot water desired temperature
• Room Setpoint M2 (H:9) – normal room temperature setpoint for circuit M2
• Room Setpoint M3 (H:10) – normal room temperature setpoint for circuit M3
• Reduced Setpoint M2 (H:12) – reduced (eco) room temperature setpoint for circuit M2
• Reduced Setpoint M3 (H:13) – reduced (eco) room temperature setpoint for circuit M3

Party and economy modes

• Party Mode A1M1 (D:60) – read-only party mode status for A1M1
• Party Mode M2 (C:12) – read/write party mode switch for M2
• Party Mode M3 (D:62) – read-only party mode status for M3
• Economy Mode M2 (C:9) – read/write economy (reduced) mode switch for M2
• Economy Mode M3 (C:3) – read/write economy (reduced) mode switch for M3

Circulation pump monitoring

• Circulation Pump A1M1 (D:14) – read-only pump status for heating circuit A1M1
• Circulation Pump M2 (D:26) – read-only pump status for heating circuit M2
• Circulation Pump M3 (D:38) – read-only pump status for heating circuit M3

Solar system monitoring

• Solar Collector Temperature (A:150) – collector panel temperature
• Solar Storage Temperature (A:151) – buffer storage temperature
• Solar Heat Yield (A:152) – cumulative solar energy production in kWh
• Solar Operating Hours (A:153) – cumulative solar system operating hours
• Solar Pump (D:59) – read-only solar circulation pump status

Additional capabilities

The Vitotronic 200 HK3B also exposes registers for boiler water temperature, effective boiler setpoint, burner modulation, boiler operating mode, and extended heating circuit operating programs. These can be added in a future template update by selecting additional data points in the Vitogate web interface.

The boiler water temperature (Kesseltemperatur) is not included in the current template. To monitor it, add the corresponding LON data point in the Vitogate web interface and create a custom Modbus device in TapHome using the newly assigned register number.

Troubleshooting

Status LED flashes orange (no configuration)

1. Access the web interface at http://169.254.0.1
2. Go to General > Vitogate and verify the Vitogate type is set to “Vitogate 300 MB (Modbus)”
3. Go to VI LON > Scan participants and scan for Vitotronic controllers
4. Select data points and save

No Modbus communication

1. Check RS-485 cables:
   • B+ (Data+) correctly connected to A+/D+ on TapHome
   • A- (Data-) correctly connected to B-/D- on TapHome
   • AGND connected to TapHome ground
2. Verify the Modbus Slave address in the Vitogate web interface matches TapHome
3. Check DIP switch 3 termination – enable only on the last device on the bus
4. Confirm TapHome is set to: 9600 baud, no parity, 1 stop bit
5. Try Modbus TCP/IP via the LAN port (port 502) as an alternative

Register values are incorrect or shifted

1. The Vitogate 300 assigns registers dynamically. If data point selection was changed, register numbers shift
2. Go to Modbus > Objects in the web interface and compare the register map with the TapHome template
3. If registers don’t match, re-select the correct LON data points to match the template’s expected mapping

LON communication errors

1. Check RJ45 LON cables between Vitogate and Vitotronic
2. Verify terminal end resistors are installed at both ends of the LON bus
3. Ensure the LON communication module is installed in the Vitotronic controller
4. Check LON system number and participant numbers (Code “77:x” and “98:x” on the Vitotronic)