2026.9.1
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Flexit

The Flexit integrationIntegrations connect and integrate Home Assistant with your devices, services, and more. [Learn more] connects Flexit air handling units equipped with a CI66 Modbus adapter to Home Assistant.

Prerequisites

Your Flexit unit needs a CI66 Modbus adapter. Depending on how the adapter is connected, you need one of the following:

  • Serial (Modbus RTU): The CI66 adapter is connected through an RS-485 interface. You can use a USB-to-RS485 converter connected to your Home Assistant host. Alternatively, as an experimental option, an ESPHome Serial Proxy with an RS-485 interface can expose the connection to Home Assistant as a network-attached serial port.
  • Network (Modbus TCP) via bridge: The CI66 adapter is wired to a Modbus TCP bridge or gateway on your network.

Configuration

To add the Flexit device to your Home Assistant instance, use this My button:

Manual configuration steps

If the above My button doesn’t work, you can also perform the following steps manually:

When you set up the integration, you’re asked to choose between a serial or a network connection.

Serial device

The serial device your Flexit CI66 Modbus adapter is connected to. Only shown for a serial connection.

Baud rate

The baud rate of the serial connection. Defaults to 57600. Only shown for a serial connection.

Host

The hostname or IP address of your Flexit CI66 Modbus bridge. Only shown for a network connection.

Port

The port of your Flexit CI66 Modbus bridge. Defaults to 502. Only shown for a network connection.

Unit ID

The Modbus unit ID of your Flexit unit. Enter a value from 1 through 32.

Note

Home Assistant can share a Modbus connection between integrations when their connection settings are compatible. If another integration uses the same connection with incompatible settings, setup fails with a connection error.

Migrating from YAML configuration

If you previously configured this integration through configuration.yamlThe configuration.yaml file is the main configuration file for Home Assistant. It lists the integrations to be loaded and their specific configurations. In some cases, the configuration needs to be edited manually directly in the configuration.yaml file. Most integrations can be configured in the UI. [Learn more], it can’t be imported automatically. The Modbus connection details used to live in a separate modbus: section, which isn’t accessible from the climate platform configuration.

  1. Remove the flexit entry under climate: from your configuration.yamlThe configuration.yaml file is the main configuration file for Home Assistant. It lists the integrations to be loaded and their specific configurations. In some cases, the configuration needs to be edited manually directly in the configuration.yaml file. Most integrations can be configured in the UI. [Learn more] file.
  2. Set up the integration again from the Home Assistant UI, providing the Modbus connection details and unit ID of your Flexit unit.
  3. Restart Home Assistant.

A repair issue in Settings > Devices & services will guide you through the same steps.

Supported functionality

Climate

The integration adds a climate entity for the Flexit unit. You can set a target temperature and choose a fan mode (Off, Low, Medium, or High). The current activity, such as heating, cooling, or idle, is shown as the entity’s HVAC action.

Data updates

The Flexit integration pollsData polling is the process of querying a device or service at regular intervals to check for updates or retrieve data. By defining a custom polling interval, you can control how frequently your system checks for new data, which can help optimize performance and reduce unnecessary network traffic. [Learn more] the unit every 30 seconds.

Troubleshooting

If setup fails with a connection error:

  • Make sure the serial device or host and port are correct and reachable from Home Assistant.
  • Make sure no other integration is already using the same connection with different settings.
  • Make sure the unit ID matches the Modbus address configured on your CI66 adapter.

Removing the integration

This integration follows standard integration removal.

To remove an integration instance from Home Assistant

  1. Go to Settings > Devices & services and select the integration card.
  2. From the list of devices, select the integration instance you want to remove.
  3. Next to the entry, select the three dots menu. Then, select Delete.