weider-modbus

Async Python library for the Modbus TCP interface of Weider WT16 heat pumps, built on modbus-connection.

The library only reads and writes registers. It takes a ModbusUnit and never opens a connection itself, so it works over any modbus-connection backend (tmodbus, pymodbus, or the in-memory mock). It is used by the Weider WT16 Home Assistant integration.

Installation

pip install weider-modbus

The library depends only on the backend-neutral modbus-connection interface. To open a connection yourself, also install a backend:

pip install "modbus-connection[tmodbus]"

Usage

import asyncio

from modbus_connection import ModbusTcpParams
from modbus_connection.tmodbus import ModbusConnection

from weider_modbus import WeiderWT16, plausible_temperature


async def main() -> None:
    connection = ModbusConnection(ModbusTcpParams(host="192.168.1.50", port=502))
    try:
        device = WeiderWT16(connection.for_unit(1))
        await device.async_update()

        print("Hot water:", device.measurements.hot_water_temperature)
        outdoor = plausible_temperature(device.measurements.outdoor_temperature)
        print("Outdoor:", outdoor)
        print("Compressor running:", device.digital_inputs.compressor)
        print("SG Ready mode:", device.sg_ready_mode)

        await device.async_set_hot_water_target(47.5)
    finally:
        await connection.close()


asyncio.run(main())

Components

A value reads as None until the first successful poll, or if the device does not provide the register.

Optional registers

The room temperature is read from input register 12 (BET.T.A.1, the measured sensor value) of the standard Modbus map.

Some firmware versions do not provide every register. The room temperature, room target, mixer position, runtimes, active error text and any digital input are optional. If the device rejects one of them with an illegal data address, the library drops that register on the first poll and stops reading it. Any other register error still raises, so real problems are not hidden.

Errors

async_update() raises a modbus_connection.ModbusError subclass (or TimeoutError / OSError from the transport) when a poll fails. The shared connection reopens on the next request, so the caller can simply retry.

The target setters raise ValueError for a value outside the allowed range (hot water 15–55 °C, room 15–35 °C), before anything is written.

Helpers

• plausible_temperature(value) returns None for the placeholder values the device reports for an unconnected sensor (outside −45 to 150 °C).
• clean_error_text(value) strips the padding from the active error text and returns None when there is no error.
• sg_ready_mode(...) and device.sg_ready_mode derive the SG Ready operating state (BZ1–BZ4) from the digital inputs.

Hardware verification

The register addresses, the signed 0.1 °C temperature format and the multi-register word order come from the existing integration. Confirm them against your WT16 documentation, especially for negative temperatures. The test simulator checks the software against this map, not the map against a real heat pump.

Development

Requires Python 3.13 or newer and uv.

uv sync
uv run pytest
uv run ruff check .
uv run ruff format --check .
uv run mypy

To run the synthetic WT16 on port 5020 for manual testing:

uv run python -m tests.simulator

Releasing

Releases are published to PyPI from GitHub Actions with trusted publishing.

1. Set the new version in pyproject.toml and merge it to main.
2. Create a GitHub release with a tag equal to that version (for example 0.1.0).
3. The Publish workflow builds the package and uploads it to PyPI.

A version number can be published only once.

License

MIT. See LICENSE.