diff --git a/homeassistant/components/opentherm_gw/__init__.py b/homeassistant/components/opentherm_gw/__init__.py
index c7a52e3d5d3..d5dae367959 100644
--- a/homeassistant/components/opentherm_gw/__init__.py
+++ b/homeassistant/components/opentherm_gw/__init__.py
@@ -32,6 +32,7 @@ from homeassistant.helpers import (
     config_validation as cv,
     device_registry as dr,
     entity_registry as er,
+    issue_registry as ir,
 )
 from homeassistant.helpers.dispatcher import async_dispatcher_send
 from homeassistant.helpers.typing import ConfigType
@@ -68,6 +69,7 @@ from .const import (
 
 _LOGGER = logging.getLogger(__name__)
 
+# *_SCHEMA required for deprecated import from configuration.yaml, can be removed in 2025.4.0
 CLIMATE_SCHEMA = vol.Schema(
     {
         vol.Optional(CONF_PRECISION): vol.In(
@@ -159,8 +161,20 @@ async def async_setup_entry(hass: HomeAssistant, config_entry: ConfigEntry) -> b
     return True
 
 
+# Deprecated import from configuration.yaml, can be removed in 2025.4.0
 async def async_setup(hass: HomeAssistant, config: ConfigType) -> bool:
     """Set up the OpenTherm Gateway component."""
+    if DOMAIN in config:
+        ir.async_create_issue(
+            hass,
+            DOMAIN,
+            "deprecated_import_from_configuration_yaml",
+            breaks_in_ha_version="2025.4.0",
+            is_fixable=False,
+            is_persistent=False,
+            severity=ir.IssueSeverity.WARNING,
+            translation_key="deprecated_import_from_configuration_yaml",
+        )
     if not hass.config_entries.async_entries(DOMAIN) and DOMAIN in config:
         conf = config[DOMAIN]
         for device_id, device_config in conf.items():
diff --git a/homeassistant/components/opentherm_gw/config_flow.py b/homeassistant/components/opentherm_gw/config_flow.py
index 3cf8a1c4594..1f52b47cbad 100644
--- a/homeassistant/components/opentherm_gw/config_flow.py
+++ b/homeassistant/components/opentherm_gw/config_flow.py
@@ -95,6 +95,7 @@ class OpenThermGwConfigFlow(ConfigFlow, domain=DOMAIN):
         """Handle manual initiation of the config flow."""
         return await self.async_step_init(user_input)
 
+    # Deprecated import from configuration.yaml, can be removed in 2025.4.0
     async def async_step_import(self, import_data: dict[str, Any]) -> ConfigFlowResult:
         """Import an OpenTherm Gateway device as a config entry.
 
diff --git a/homeassistant/components/opentherm_gw/strings.json b/homeassistant/components/opentherm_gw/strings.json
index b23e1eb7687..f0573db0531 100644
--- a/homeassistant/components/opentherm_gw/strings.json
+++ b/homeassistant/components/opentherm_gw/strings.json
@@ -316,6 +316,12 @@
       }
     }
   },
+  "issues": {
+    "deprecated_import_from_configuration_yaml": {
+      "title": "Deprecated configuration",
+      "description": "Configuration of the OpenTherm Gateway integration through configuration.yaml is deprecated. Your configuration has been migrated to config entries. Please remove any OpenTherm Gateway configuration from your configuration.yaml."
+    }
+  },
   "options": {
     "step": {
       "init": {
diff --git a/tests/components/opentherm_gw/test_config_flow.py b/tests/components/opentherm_gw/test_config_flow.py
index 4f4a6cfce31..57bea4e55dc 100644
--- a/tests/components/opentherm_gw/test_config_flow.py
+++ b/tests/components/opentherm_gw/test_config_flow.py
@@ -54,6 +54,7 @@ async def test_form_user(
     assert mock_pyotgw.return_value.disconnect.await_count == 1
 
 
+# Deprecated import from configuration.yaml, can be removed in 2025.4.0
 async def test_form_import(
     hass: HomeAssistant,
     mock_pyotgw: MagicMock,
diff --git a/tests/components/opentherm_gw/test_init.py b/tests/components/opentherm_gw/test_init.py
index 4085e25c614..3e85afbf782 100644
--- a/tests/components/opentherm_gw/test_init.py
+++ b/tests/components/opentherm_gw/test_init.py
@@ -4,13 +4,18 @@ from unittest.mock import MagicMock
 
 from pyotgw.vars import OTGW, OTGW_ABOUT
 
+from homeassistant import setup
 from homeassistant.components.opentherm_gw.const import (
     DOMAIN,
     OpenThermDeviceIdentifier,
 )
 from homeassistant.const import CONF_ID
 from homeassistant.core import HomeAssistant
-from homeassistant.helpers import device_registry as dr, entity_registry as er
+from homeassistant.helpers import (
+    device_registry as dr,
+    entity_registry as er,
+    issue_registry as ir,
+)
 
 from .conftest import MOCK_GATEWAY_ID, VERSION_TEST
 
@@ -148,3 +153,25 @@ async def test_climate_entity_migration(
         updated_entry.unique_id
         == f"{mock_config_entry.data[CONF_ID]}-{OpenThermDeviceIdentifier.THERMOSTAT}-thermostat_entity"
     )
+
+
+# Deprecation test, can be removed in 2025.4.0
+async def test_configuration_yaml_deprecation(
+    hass: HomeAssistant,
+    issue_registry: ir.IssueRegistry,
+    mock_config_entry: MockConfigEntry,
+    mock_pyotgw: MagicMock,
+) -> None:
+    """Test that existing configuration in configuration.yaml creates an issue."""
+
+    await setup.async_setup_component(
+        hass, DOMAIN, {DOMAIN: {"legacy_gateway": {"device": "/dev/null"}}}
+    )
+
+    await hass.async_block_till_done()
+    assert (
+        issue_registry.async_get_issue(
+            DOMAIN, "deprecated_import_from_configuration_yaml"
+        )
+        is not None
+    )