diff --git a/homeassistant/components/generic_thermostat/climate.py b/homeassistant/components/generic_thermostat/climate.py
index 7062267de19..3c7959dbf4d 100644
--- a/homeassistant/components/generic_thermostat/climate.py
+++ b/homeassistant/components/generic_thermostat/climate.py
@@ -266,6 +266,14 @@ class GenericThermostat(ClimateEntity, RestoreEntity):
         if not self._hvac_mode:
             self._hvac_mode = HVAC_MODE_OFF
 
+        # Prevent the device from keep running if HVAC_MODE_OFF
+        if self._hvac_mode == HVAC_MODE_OFF and self._is_device_active:
+            await self._async_heater_turn_off()
+            _LOGGER.warning(
+                "The climate mode is OFF, but the switch device is ON. Turning off device %s",
+                self.heater_entity_id,
+            )
+
     @property
     def should_poll(self):
         """Return the polling state."""
@@ -418,7 +426,11 @@ class GenericThermostat(ClimateEntity, RestoreEntity):
     async def _async_control_heating(self, time=None, force=False):
         """Check if we need to turn heating on or off."""
         async with self._temp_lock:
-            if not self._active and None not in (self._cur_temp, self._target_temp):
+            if not self._active and None not in (
+                self._cur_temp,
+                self._target_temp,
+                self._is_device_active,
+            ):
                 self._active = True
                 _LOGGER.info(
                     "Obtained current and target temperature. "
@@ -480,6 +492,9 @@ class GenericThermostat(ClimateEntity, RestoreEntity):
     @property
     def _is_device_active(self):
         """If the toggleable device is currently active."""
+        if not self.hass.states.get(self.heater_entity_id):
+            return None
+
         return self.hass.states.is_state(self.heater_entity_id, STATE_ON)
 
     @property
diff --git a/tests/components/generic_thermostat/test_climate.py b/tests/components/generic_thermostat/test_climate.py
index b83828c86c7..dc5353971b7 100644
--- a/tests/components/generic_thermostat/test_climate.py
+++ b/tests/components/generic_thermostat/test_climate.py
@@ -1249,6 +1249,92 @@ async def test_no_restore_state(hass):
     assert state.state == HVAC_MODE_OFF
 
 
+async def test_initial_hvac_off_force_heater_off(hass):
+    """Ensure that restored state is coherent with real situation.
+
+    'initial_hvac_mode: off' will force HVAC status, but we must be sure
+    that heater don't keep on.
+    """
+    # switch is on
+    calls = _setup_switch(hass, True)
+    assert hass.states.get(ENT_SWITCH).state == STATE_ON
+
+    _setup_sensor(hass, 16)
+
+    await async_setup_component(
+        hass,
+        DOMAIN,
+        {
+            "climate": {
+                "platform": "generic_thermostat",
+                "name": "test_thermostat",
+                "heater": ENT_SWITCH,
+                "target_sensor": ENT_SENSOR,
+                "target_temp": 20,
+                "initial_hvac_mode": HVAC_MODE_OFF,
+            }
+        },
+    )
+    await hass.async_block_till_done()
+    state = hass.states.get("climate.test_thermostat")
+    # 'initial_hvac_mode' will force state but must prevent heather keep working
+    assert state.state == HVAC_MODE_OFF
+    # heater must be switched off
+    assert len(calls) == 1
+    call = calls[0]
+    assert call.domain == HASS_DOMAIN
+    assert call.service == SERVICE_TURN_OFF
+    assert call.data["entity_id"] == ENT_SWITCH
+
+
+async def test_restore_will_turn_off_(hass):
+    """Ensure that restored state is coherent with real situation.
+
+    Thermostat status must trigger heater event if temp raises the target .
+    """
+    heater_switch = "input_boolean.test"
+    mock_restore_cache(
+        hass,
+        (
+            State(
+                "climate.test_thermostat",
+                HVAC_MODE_HEAT,
+                {ATTR_TEMPERATURE: "18", ATTR_PRESET_MODE: PRESET_NONE},
+            ),
+            State(heater_switch, STATE_ON, {}),
+        ),
+    )
+
+    hass.state = CoreState.starting
+
+    assert await async_setup_component(
+        hass, input_boolean.DOMAIN, {"input_boolean": {"test": None}}
+    )
+    await hass.async_block_till_done()
+    assert hass.states.get(heater_switch).state == STATE_ON
+
+    _setup_sensor(hass, 22)
+
+    await async_setup_component(
+        hass,
+        DOMAIN,
+        {
+            "climate": {
+                "platform": "generic_thermostat",
+                "name": "test_thermostat",
+                "heater": heater_switch,
+                "target_sensor": ENT_SENSOR,
+                "target_temp": 20,
+            }
+        },
+    )
+    await hass.async_block_till_done()
+    state = hass.states.get("climate.test_thermostat")
+    assert state.attributes[ATTR_TEMPERATURE] == 20
+    assert state.state == HVAC_MODE_HEAT
+    assert hass.states.get(heater_switch).state == STATE_ON
+
+
 async def test_restore_state_uncoherence_case(hass):
     """
     Test restore from a strange state.