Viessmann
Vitodens Boilers and Vitocal Heat Pumps — Modbus KNX Integration and SG Ready
Viessmann (Allendorf, Germany, founded 1917, acquired by Carrier Global 2023) is Europe's second-largest heating manufacturer. Vitodens 200-W gas condensing boiler integrates with KNX via Modbus TCP (ViCARE ModBus module) — boiler setpoint, return temperature, and fault status as KNX GAs. Vitocal heat pump range (Vitocal 250-A, 300-A, R32) supports SG Ready 2-wire input for PV surplus control, connected to KNX binary output relay.
Role in our panels
How we use Viessmann
Vitodens 200-W Modbus: ViCARE ModBus module (DIN-rail, RS-485 or Ethernet RJ45), holds registers: 1=flow setpoint (°C×10), 3=return temperature (read-only), 5=boiler status (0=standby, 1=heating, 2=DHW), 100=fault code. KNX/Modbus gateway (Intesis or MDT) maps registers to KNX GAs. ETS6 logic: KNX thermostat setpoint → Modbus register 1 write → boiler adjusts flow temperature. Vitocal heat pump SG Ready: SG Ready 2-wire input (S1/S2 dry contacts) on Vitocal outdoor unit PCB. Connect KNX binary output relay: State 2 normal (S1=0, S2=0), State 3 encouraged (S1=0, S2=1, high COP operation), State 4 maximum (S1=1, S2=1, maximum PV utilisation). Trigger: Fronius Modbus surplus >3kW → KNX relay S2=1. Vitocal also supports direct Modbus TCP via VitoConnect 200 gateway — higher integration resolution than SG Ready relay. ViCare API and cloud integration: Viessmann ViCare REST API (api.viessmann.com, OAuth2) provides historical energy data (heating kWh, COP, DHW temperature) for non-critical monitoring. Home Assistant Viessmann integration polls API every 5 minutes → publishes to KNX GAs via HA KNX integration. Not suitable for real-time control (5-minute latency) — use local Modbus for control, ViCare API for energy reporting. Market position: Viessmann Vitodens is the dominant gas boiler in Germany, Austria, Switzerland. Vitocal heat pumps compete with Vaillant arotherm and Nibe F2080 in the European heat pump market. KNX integration is most common in commercial buildings (office heating circuits, hotel hot water) where BMS Modbus connection to boiler plant is standard practice.
Modbus TCP integration via ViCARE ModBus module — flow setpoint write, return temperature and fault code monitoring as KNX GAs. Vitocal heat pump SG Ready relay input for KNX PV surplus optimisation.
Used in these project types
Viessmann products
Key components we install
Vitodens 200-W 26kW
Wall-hung gas condensing boiler, 26kW output, ErP A-rated. Integrates with KNX via ViCARE ModBus module (sold separately) over RS-485 or Ethernet Modbus TCP. Flow setpoint writable via register 1 (°C×10), return temperature and fault code readable. Used in residential and small commercial heating systems where KNX BMS setpoint control is required.
ViCARE ModBus module
DIN-rail Modbus interface for Vitodens boilers. Connects via RS-485 (RTU, 9600 baud) or Ethernet (Modbus TCP, port 502) — configured via DIP switches. Exposes Viessmann boiler registers: flow setpoint (rw), return temperature (ro), boiler status (ro), fault code (ro). Paired with KNX/Modbus gateway (Intesis or MDT) for KNX group address mapping in ETS6.
Vitocal 250-A 8kW
Monobloc air-source heat pump, 8kW (A7/W35), R32 refrigerant, ErP A+++ rated. SG Ready 2-wire dry-contact input on outdoor unit PCB for PV surplus integration via KNX binary output relay. Three operating states: normal, encouraged (high COP), maximum (full PV utilisation). Suitable for new-build residential and retrofit projects with KNX solar optimisation logic.
Vitocal 300-A 13kW
Air-water heat pump, 13kW (A7/W35), R32, Modbus TCP via VitoConnect 200 gateway for higher-resolution KNX integration beyond SG Ready binary control. Supports direct flow temperature setpoint control and COP monitoring via Modbus registers. Used in larger residential villas and small commercial buildings with detailed energy management requirements.
VitoConnect 200
Ethernet communication gateway for Vitocal heat pumps — enables Modbus TCP access and ViCare cloud connectivity. Provides higher integration resolution than SG Ready relay: direct register-level control of heat pump setpoint, mode, and DHW target. Also enables ViCare REST API access for historical energy reporting via Home Assistant.
Viessmann FAQ
Does Viessmann ViCARE ModBus support both RTU and TCP?
ViCARE ModBus module supports RS-485 (RTU, 9600 baud) and Ethernet (Modbus TCP, port 502) — configure via module DIP switches. Use Modbus TCP for longer distances and better network integration; RS-485 for direct connection to MDT or WAGO Modbus gateway.
Can KNX control individual Viessmann heating zones?
Yes — if the Viessmann system uses a zone controller (Vitotronic 200, HK3 variant) with zone pump outputs, KNX binary output relays can control zone pump contactors. For direct zone setpoint control, use ViCARE ModBus registers for each zone circuit setpoint.
Viessmann vs Vaillant for KNX integration?
Both support similar Modbus integration chains. Vaillant uses eBUS protocol on older models (gateway required). Viessmann ViCARE ModBus is more straightforward — direct Modbus TCP without proprietary protocol conversion. Choose based on local installer preference and installed base.
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