The Vallox MV series (51, 96, 99, 101, 110, 125, 139, 145, 245 MV and ValloPlus variants) are mechanical ventilation heat recovery (MVHR) units. TapHome connects via Modbus TCP, but the MyVallox Control does not have a native Modbus TCP option — an RS-485 Modbus RTU-to-TCP gateway (such as Elfin EW11 or USR-W610) is required between the ventilation unit and TapHome Core.
The template provides comprehensive control: Home/Away mode switching, Boost mode with timer, fan speed settings per mode, five temperature sensors, humidity and CO2 monitoring, weekly timer, and per-mode temperature targets with thermostat control.
Hardware connection
The Vallox unit exposes a Modbus RTU interface on the X102 connector board. Up to 32 units can be daisy-chained on a single RS-485 bus. A 120 Ohm termination resistor is required at the last unit on the bus.
- Protocol: Modbus RTU (RS-485)
- Connector: X102 terminal block (A and B terminals)
- Max units per bus: 32
- Termination: 120 Ohm resistor at the end of the bus
The MyVallox Control does not support Modbus TCP natively. A Modbus RTU-to-TCP gateway must be placed between the Vallox unit’s RS-485 bus and TapHome Core’s Ethernet network. Configure the gateway with matching serial parameters (default: 19200 baud, even parity, 1 stop bit).
Wiring diagram
The wiring diagram shows the RS-485 bus connection using the X102 connector on each Vallox unit. Connect wire A to terminal A and wire B to terminal B. The Modbus master (RTU-to-TCP gateway) connects at the beginning of the bus.
Enabling Modbus communication
Modbus settings must be configured on the ventilation unit before TapHome can communicate. The following parameters are required:
| Setting | Options | Default |
|---|---|---|
| Modbus address | 1–247 | 1 |
| Baud rate | 9600, 19200, 38400, 57600, 115200 | 19200 |
| Parity | no, even, odd | even |
| Stop bit | 1 or 2 | 1 |
Via MyVallox Control panel
- Select Settings and navigate to Expert settings
- Select Modbus settings and press OK
- Screen 1/4: Set Modbus address (1–247) using +/- buttons
- Screen 2/4: Set baud rate (default 19200) and parity
- Screen 3/4: Set parity (no/even/odd)
- Screen 4/4: Set stop bit (1 or 2)
- Press OK to save
Via web interface
The same Modbus settings (address, baud rate, parity, stop bit) can also be configured through the MyVallox web interface — navigate to Expert settings → Modbus settings via local network or MyVallox Cloud.
Configuration
When importing the template in TapHome, provide:
- IP Address — the RTU-to-TCP gateway’s IP address on the local network
- Slave ID — Modbus address of the Vallox unit (default: 1)
Assign a static IP address to the RTU-to-TCP gateway in the router’s DHCP settings. The gateway’s serial port must be configured with the same parameters as the Vallox unit (default: 19200 baud, even parity, 1 stop bit).
Device capabilities
The template exposes 34 devices organized into operating mode control, fan speed management, temperature monitoring, air quality sensors, timer controls, and per-mode configuration profiles.
Operating mode control
Vallox uses two basic modes (Home and Away) — one is always active. Three timed modes (Boost, Fireplace, Programmable) can temporarily override the basic mode.
- State (Home/Away) — toggle switch for the active basic mode via register H:4609. Write 0 for Home, 1 for Away.
- Mode (Override State) — multi-value switch on register H:4610. Write 0 for Normal operation, 5 to switch the unit off.
Mode priority when multiple modes are active simultaneously:
- Programmable mode (highest)
- Fireplace mode
- Boost mode
- Home/Away basic mode (lowest)
Fan speed control
Fan speed is configured separately for each operating mode as a percentage (0–100%):
- Fan Speed (Home) — Home mode fan speed setting (H:20507)
- Fan Speed (Away) — Away mode fan speed setting (H:20501)
- Fan Speed (Boost) — Boost mode fan speed setting (H:20513)
- Current Fan Speed — read-only sensor showing the actual fan speed (H:4353)
- Current Fan Speed (Dimmer) — dimmer representation of the current fan speed (same register H:4353)
The Programmable mode has separate supply and extract fan controls:
- Programmable Mode Supply Fan Speed — supply fan speed for Programmable mode (H:20495)
- Programmable Mode Extract Fan Speed — extract fan speed for Programmable mode (H:20494)
Temperature monitoring
The template includes five temperature sensors. All temperatures are stored in centKelvins and converted automatically: Celsius = register_value / 100 - 273.15.
| Device | Register | Description |
|---|---|---|
| Outdoor Air Temperature | H:4356 | Outside air before entering the unit |
| Extract Air Temperature | H:4354 | Air extracted from rooms before heat recovery |
| Exhaust Air Temperature | H:4355 | Air exhausted outdoors after heat recovery |
| Supply Cell Air Temperature | H:4357 | Air inside the heat recovery cell (supply side) |
| Supply Air Temperature | H:4358 | Fresh air supplied to rooms after heat recovery |
Air quality monitoring
- Humidity — relative humidity percentage (H:4363, requires RH sensor accessory)
- CO2 Level — CO2 concentration in ppm (H:4364, requires CO2 sensor accessory)
Timer and mode controls
- Boost Remaining Time — write desired minutes to activate Boost mode, 0 to deactivate, 65535 for indefinite (H:4612)
- Boost Timer Enabled — enable/disable Boost timer countdown (H:21766)
- Weekly Timer Enabled — enable/disable weekly schedule program (H:4615)
- Defrosting — defrost cycle status indicator (H:4611)
Per-mode temperature targets
Each mode has a thermostat device that reads the current extract air temperature (H:4354) and allows setting a supply air temperature target:
- Home Mode Temperature Target — target register H:20508
- Away Mode Temperature Target — target register H:20502
- Boost Mode Temperature Target — target register H:20514
- Programmable Mode Temperature Target — target register H:20493
Per-mode air quality control
Humidity and CO2-based automatic fan speed adjustment can be enabled per mode:
- Home Mode RH Control / CO2 Control — H:20505 / H:20506
- Away Mode RH Control / CO2 Control — H:20499 / H:20500
- Boost Mode RH Control / CO2 Control — H:20511 / H:20512
Diagnostics
- Cell State — heat recovery cell operating state (H:4616)
- Remaining Time for Filter — days until filter replacement (H:4620)
- Command Variable — special command register for maintenance operations (H:4627)
- Programmable Mode Duration — default duration for Programmable mode in minutes (H:20496)
Additional capabilities
The Vallox units also expose Modbus registers for fireplace mode timer control (H:4613), programmable mode timer (H:4614), fault condition reporting (H:4621), individual supply/extract fan speed monitoring, fireplace mode fan speed configuration, filter change interval settings, and optional external temperature sensor input. These can be added to the TapHome template in a future update.
Troubleshooting
No Modbus communication
- Verify the RS-485 wiring on the X102 connector — check A/B terminal polarity
- Confirm the RTU-to-TCP gateway serial parameters match the Vallox unit (default: 19200 baud, even parity, 1 stop bit)
- Ensure the gateway IP address is correct and reachable from TapHome Core
- Check that the Modbus slave address matches between the Vallox unit and TapHome configuration
Temperature readings show incorrect values
All temperature registers use centKelvin encoding. The TapHome template handles the conversion automatically (value / 100 - 273.15). If raw values appear instead of Celsius, verify the template was imported correctly.
Mode changes not applied
During active defrost cycles, the unit may ignore mode write commands. The Defrosting switch (H:4611) indicates when defrost is active. Wait for the cycle to complete before changing modes. Additionally, check mode priority — a higher-priority timed mode overrides lower-priority modes.
Boost mode does not deactivate
Write 0 to register H:4612 (Boost Remaining Time) to stop Boost mode. If the Boost Timer Enabled switch (H:21766) was set to 0 (disabled), the timer countdown was disabled and Boost runs indefinitely until manually stopped.
