Ochsner BWWP Genius 333
The Ochsner BWWP Genius 333 is a compact domestic hot water heat pump with a 300-litre integrated tank, designed for residential PV self-consumption. The template reads tank temperature and the unit's own calculated surplus power via Modbus RTU, and writes a PV surplus power setpoint to steer the internal electric heating element. Monitoring these registers in the ModbusCloud portal gives installers continuous visibility into hot water production and surplus utilisation, without polling the device manually.
- Protocol
- Modbus RTU
- Connection
- RS485
- Registers
- 4, read and write
- Brand
- Ochsner
- Last updated
Registers (4)
3 read, 1 write
| Name | Unit | Access | Address (Hidden until you enter your email) | Function (hidden) | Type (hidden) |
|---|---|---|---|---|---|
| setmaxpower_a | W | Read | |||
| setmaxpower_b | W | Write | |||
| temp | °C | Read | |||
| limittemp | °C | Read |
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Use cases
- Monitor hot water tank temperature continuously to detect heating failures or setpoint deviations.
- Track the calculated surplus power register to verify the Genius 333 is receiving the correct PV excess signal.
- Alert when tank temperature drops below the anti-legionella limit temperature for more than a configured interval.
- Compare the written surplus power setpoint against the read-back calculated value to confirm register writes succeed.
- Report daily surplus energy absorption to assess how much PV generation is being shifted into hot water.
Installation
Enable Modbus on the Genius 333 by navigating to the communication or Modbus section in the Tiptronic plus S controller menu and setting the Modbus slave address and baud rate.
Connect the RS485 terminals on connector X3 of the heat pump to the ModbusCloud Gateway using a shielded two-wire cable, observing A/B polarity and fitting a termination resistor at each end of the bus.
In the ModbusCloud portal, add the Gateway, import the Ochsner BWWP Genius 333 template, and set the unit ID to match the slave address configured on the device.
Verify the connection by checking that the temp register (address 2000) returns a plausible hot water temperature; if the value is zero or negative, confirm half-duplex RS485 mode is selected in the Gateway settings.
Things to watch for
Why does the surplus power register keep accumulating instead of tracking my input?
The setmaxpower_b register (address 2201) must be written as a signed 16-bit big-endian integer. Writing it as an unsigned value prevents negative numbers from reaching the unit, so the device's internal accumulator never decrements and the heating element stays at maximum power regardless of the value sent.
The gateway connects but no values appear on the temp register. What now?
The Genius 333 uses Modbus RTU over RS485 in half-duplex mode. If your RS485 adapter is set to full-duplex, the device will not respond. Switch the adapter or Gateway RS485 port to half-duplex mode. Also confirm the termination resistor jumper on the heat pump board is set correctly.
How often must I write the surplus power setpoint to keep the heating element active?
Ochsner documentation requires the surplus power value to be refreshed at least every 5 to 10 seconds. If the register is not updated within approximately 10 minutes, the unit times out and stops the electric heating element as a safety measure. ModbusCloud writes registers at most once per minute, so it cannot follow this 5 to 10 second refresh. Surplus control of this unit through ModbusCloud is therefore not guaranteed, while reading its values works.
Is it safe to write any value to the surplus power setpoint register?
Write only values that reflect actual measured PV surplus, in watts, as a signed 16-bit integer. Sending an excessively large setpoint will drive the heating element to its maximum continuously and may cause the unit to reach its thermal limit, trip protection circuits, or heat water beyond the configured maximum temperature. Always test setpoint changes in small increments.
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