diff --git a/homeassistant/components/generic_thermostat/climate.py b/homeassistant/components/generic_thermostat/climate.py
index 4072c43bc27..175ee8f1d5b 100644
--- a/homeassistant/components/generic_thermostat/climate.py
+++ b/homeassistant/components/generic_thermostat/climate.py
@@ -33,7 +33,7 @@ from homeassistant.const import (
     STATE_UNAVAILABLE,
     STATE_UNKNOWN,
 )
-from homeassistant.core import DOMAIN as HA_DOMAIN, callback
+from homeassistant.core import DOMAIN as HA_DOMAIN, CoreState, callback
 from homeassistant.helpers import condition
 import homeassistant.helpers.config_validation as cv
 from homeassistant.helpers.event import (
@@ -207,7 +207,7 @@ class GenericThermostat(ClimateEntity, RestoreEntity):
             )
 
         @callback
-        def _async_startup(event):
+        def _async_startup(*_):
             """Init on startup."""
             sensor_state = self.hass.states.get(self.sensor_entity_id)
             if sensor_state and sensor_state.state not in (
@@ -215,8 +215,12 @@ class GenericThermostat(ClimateEntity, RestoreEntity):
                 STATE_UNKNOWN,
             ):
                 self._async_update_temp(sensor_state)
+                self.async_write_ha_state()
 
-        self.hass.bus.async_listen_once(EVENT_HOMEASSISTANT_START, _async_startup)
+        if self.hass.state == CoreState.running:
+            _async_startup()
+        else:
+            self.hass.bus.async_listen_once(EVENT_HOMEASSISTANT_START, _async_startup)
 
         # Check If we have an old state
         old_state = await self.async_get_last_state()
diff --git a/tests/components/generic_thermostat/test_climate.py b/tests/components/generic_thermostat/test_climate.py
index eaf7c8e5651..71c6f41282b 100644
--- a/tests/components/generic_thermostat/test_climate.py
+++ b/tests/components/generic_thermostat/test_climate.py
@@ -209,6 +209,30 @@ async def test_setup_defaults_to_unknown(hass):
     assert HVAC_MODE_OFF == hass.states.get(ENTITY).state
 
 
+async def test_setup_gets_current_temp_from_sensor(hass):
+    """Test that current temperature is updated on entity addition."""
+    hass.config.units = METRIC_SYSTEM
+    _setup_sensor(hass, 18)
+    await hass.async_block_till_done()
+    await async_setup_component(
+        hass,
+        DOMAIN,
+        {
+            "climate": {
+                "platform": "generic_thermostat",
+                "name": "test",
+                "cold_tolerance": 2,
+                "hot_tolerance": 4,
+                "heater": ENT_SWITCH,
+                "target_sensor": ENT_SENSOR,
+                "away_temp": 16,
+            }
+        },
+    )
+    await hass.async_block_till_done()
+    assert hass.states.get(ENTITY).attributes["current_temperature"] == 18
+
+
 async def test_default_setup_params(hass, setup_comp_2):
     """Test the setup with default parameters."""
     state = hass.states.get(ENTITY)