# Set up with Serin Link

> Use Serin Link to control your indoor unit, with or without a smart-home app, and supply the room temperature.

Source: https://serin-labs.com/controller/link.html
Last updated: 2026-10-27

Serin Link controls the controller directly, with or without a smart-home app. Its pairing is separate from app pairing.

## Use Serin Link without a smart-home app

For a new controller, follow [Serin Link setup without an app](https://serin-labs.com/link/manual.html#using-link-without-a-smart-home-app). That guide uses free HomeKit-compatible firmware, labeled **Apple Home** in the flash tool. No Apple device or home hub is required.

For ESPHome or Matter-compatible firmware, use the existing-controller pairing route.

The controller ships ready to flash; ordering it with Serin Link does not pair them. Serin Link control works without Wi-Fi; web access and apps need network setup.

## Add Serin Link to an existing controller

Serin Link works with the standard ESPHome, HomeKit-compatible and Matter-compatible builds on both NanoC6 and Atom S3 Lite. A custom ESPHome configuration must include Serin Link support.

Follow [Pair your first controller](https://serin-labs.com/link/pairing.html) for your installed firmware.

## Use Serin Link as the room temperature source

After pairing, select Serin Link as the temperature source to use its reading.

On HomeKit-compatible and Matter-compatible firmware, select it in **Room Sensor**. See [configure temperature sources](https://serin-labs.com/controller/sensors-web.html).

### Select Serin Link in ESPHome

The standard ESPHome build includes Serin Link sensor support. In generated YAML, enable both the connection and room-temperature sensor options under **Serin Link**; see [Customize ESPHome](https://serin-labs.com/controller/customize-esphome.html).

On Serin Link, open **Settings** > **Room Sensor**, highlight **Serin Link 1**, and push the knob. Alternatively, set **Room Temperature Source** to **Serin Link 1** in Home Assistant. Select **Heat pump** to return to the built-in sensor.

Serin Link's **Temperature** and **Humidity** appear under its **Serin Link 1** device in Home Assistant regardless of the selected source.

If you enable **Home Assistant temperature sensor** in the generator, **Home Assistant** joins the source list. Its readings feed the heat pump only while selected.

## Check control and the reading

Change the target on Serin Link and confirm the indoor unit responds. If using its sensor, compare the controller's room reading with Serin Link's.

For pairing problems, use [Serin Link troubleshooting](https://serin-labs.com/link/troubleshooting.html). If the controller responds but the indoor unit does not, use [controller troubleshooting](https://serin-labs.com/troubleshooting.html#hvac-no-response).