Add initial Hot Spring integration documentation

source/_integrations/hotspring.markdown

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+---
+title: Hot Spring
+description: Instructions on how to integrate Hot Spring spas into Home Assistant.
+ha_release: 2026.8
+ha_category:
+  - Water heater
+ha_iot_class: Local Polling
+ha_codeowners:
+  - '@Moustachauve'
+ha_domain: hotspring
+ha_platforms:
+  - water_heater
+ha_integration_type: device
+---
+
+The **Hot Spring** {% term integration %} allows you to monitor and control your [Hot Spring](https://www.hotspring.com/) spa equipped with the **Connected Spa Kit 2** (Part #79994) module directly from Home Assistant.
+
+## Supported hardware
+
+- Hot Spring Spas equipped with the **HotSpring Connected Spa Kit 2** (Part #79994) local network module.
+
+## Prerequisites
+
+1. Install and set up the **HotSpring Connected Spa Kit 2** on your hot tub following the manufacturer's quick start guide.
+2. Use the official **HotSpring Connected Spa** app to connect the spa module to your home Wi-Fi or local network.
+3. Verify that your Home Assistant instance and the Hot Spring spa module are on the same local network subnet.
+
+{% include integrations/config_flow.md %}
+
+{% configuration_basic %}
+Host:
+    description: "The hostname or IP address of your Hot Spring HNA (Home Network Adapter) on your local network (for example, `192.168.1.150`)."
+{% endconfiguration_basic %}
+
+{% note %}
+When setting up or reconfiguring the integration, ensure you enter the IP address of the **HNA (Home Network Adapter)** and **not** the IP address of the **SNA (Spa Network Adapter)**.
+{% endnote %}
+
+### Reconfiguration
+
+If the IP address of your Hot Spring spa changes, you can reconfigure the integration by going to {% my integrations title="**Settings** > **Devices & services**" %}, selecting the **Hot Spring** integration, clicking {% icon "mdi:dots-vertical" %} and choosing **Reconfigure**.
+
+## Supported functionality
+
+The **Hot Spring** integration provides the following entities:
+
+### Water heater
+
+- **Water heater**
+  - **Description**: Displays the current water temperature and allows setting the target water temperature.
+  - **Temperature Range**: 80.0 °F to 104.0 °F
+  - **Remarks**: Turning the water heater on or off is not supported by the integration.
+
+## Data updates
+
+The **Hot Spring** integration uses local {% term polling %} to fetch status updates directly from the spa module on your local network.
+
+## Troubleshooting
+
+### Cannot connect to Hot Spring spa
+
+If Home Assistant cannot establish a connection to your Hot Spring spa:
+
+1. Make sure your Hot Spring spa module is powered on and connected to your local network.
+2. Verify that you are using the IP address of the **HNA (Home Network Adapter)** and not the **SNA (Spa Network Adapter)**.
+3. Verify that you can locate the device on your local network router client list.
+4. Double check that the IP address or hostname entered is correct and reachable from your Home Assistant instance.
+5. Try restarting the Hot Spring spa module and reloading the integration in Home Assistant.
+
+## Removing the integration
+
+This integration follows standard integration removal.
+
+{% include integrations/remove_device_service.md %}