Connecting Viessmann Heat Pump via Modbus to Loxone

This guide covers integrating Viessmann heat pumps with Loxone home automation via Modbus using the Vitogate module.

System Architecture

Vitogate Configuration

Accessing Vitogate Web Interface

The Vitogate uses a link-local IP address by default:

1. Connect PC directly to Vitogate via Ethernet
2. Configure PC network adapter:
   • IP: 169.254.0.10 (or any 169.254.0.x except .1)
   • Subnet: 255.255.0.0
   • Gateway: Leave blank
3. Open browser to http://169.254.0.1
4. Default credentials: admin / admin (change after setup)

Vitogate Network Settings

For Loxone integration, assign a static IP:

1. Navigate to Network Settings
2. Set static IP in your LAN subnet (e.g., 192.168.1.50)
3. Set appropriate subnet mask and gateway
4. Save and reboot Vitogate
5. Reconnect your PC to regular network
6. Access Vitogate at new IP address

Enabling Modbus TCP

1. Navigate to Interfaces > Modbus
2. Enable Modbus TCP Server
3. Set port (default 502)
4. Configure Unit ID (typically 1)
5. Save configuration

Loxone Configuration

Adding Modbus Device

1. Open Loxone Config
2. Add Modbus Server peripheral
3. Configure:
   • IP Address: Vitogate IP (e.g., 192.168.1.50)
   • Port: 502
   • Unit ID: 1 (must match Vitogate)

Common Viessmann Modbus Registers

Note: Register addresses vary by Vitogate firmware and heat pump model. Consult Vitogate Modbus documentation for exact mapping.

Function	Register Type	Typical Address	Data Type
Outside Temp	Input (3x)	30001	INT16 /10
Supply Temp	Input (3x)	30002	INT16 /10
Return Temp	Input (3x)	30003	INT16 /10
DHW Temp	Input (3x)	30004	INT16 /10
Operating Mode	Holding (4x)	40001	UINT16
Room Setpoint	Holding (4x)	40002	INT16 /10
DHW Setpoint	Holding (4x)	40003	INT16 /10
Compressor Status	Input (3x)	30010	BOOL

Creating Loxone Function Blocks

For analog values (temperatures):

1. Add Modbus Input block
2. Set register address
3. Set data type (typically Signed 16-bit)
4. Apply scaling (divide by 10 for temperatures)

For setpoints (writable):

1. Add Modbus Output block
2. Set register address (Holding register)
3. Apply reverse scaling (multiply by 10)

Troubleshooting

Cannot Access Vitogate at 169.254.0.1

Check:

• Direct Ethernet connection (no switch)
• PC IP in 169.254.0.x range (not .1)
• Disable Wi-Fi on PC
• Try different browser
• Wait 60 seconds after power-up

Modbus Connection Refused

Check:

• Vitogate IP reachable (ping test)
• Modbus TCP enabled in Vitogate
• Port 502 not blocked by firewall
• Correct Unit ID in Loxone

Values Show Zero or Incorrect

Check:

• Register addresses match Vitogate documentation
• Correct data type (signed vs unsigned)
• Scaling factor applied (most temps are value/10)
• Byte order settings if values seem corrupted

Intermittent Communication

Check:

• Network stability
• Reduce polling rate (Vitogate has limited throughput)
• Check for IP conflicts
• Verify Vitogate firmware is current

Best Practices

Polling Rates

• Temperature values: 30-60 second intervals
• Status points: 10-30 second intervals
• Avoid polling faster than 5 seconds

Register Organization

• Group related registers to minimize transactions
• Use block reads where possible
• Prioritize critical values

Data Validation

• Implement range checking in Loxone
• Set reasonable min/max limits
• Alert on communication failures

Viessmann Documentation

For register mappings, obtain:

• Vitogate 200 Modbus documentation (from Viessmann)
• Data point list for your specific heat pump model
• Firmware release notes for any register changes

Note: Viessmann may require installer access or technical support contact to obtain detailed Modbus documentation.