diff --git a/homeassistant/components/mqtt/climate.py b/homeassistant/components/mqtt/climate.py
index c8a50b523e8..99b51d2ab3e 100644
--- a/homeassistant/components/mqtt/climate.py
+++ b/homeassistant/components/mqtt/climate.py
@@ -439,6 +439,13 @@ class MqttClimate(MqttEntity, ClimateEntity):
         discovery_data: DiscoveryInfoType | None,
     ) -> None:
         """Initialize the climate device."""
+        self._attr_fan_mode = None
+        self._attr_hvac_action = None
+        self._attr_hvac_mode = None
+        self._attr_is_aux_heat = None
+        self._attr_swing_mode = None
+        self._attr_target_temperature_low = None
+        self._attr_target_temperature_high = None
         MqttEntity.__init__(self, hass, config, config_entry, discovery_data)
 
     @staticmethod
@@ -463,29 +470,23 @@ class MqttClimate(MqttEntity, ClimateEntity):
 
         self._topic = {key: config.get(key) for key in TOPIC_KEYS}
 
-        # set to None in non-optimistic mode
-        self._attr_target_temperature = None
-        self._attr_fan_mode = None
-        self._attr_hvac_mode = None
-        self._attr_swing_mode = None
-        self._attr_target_temperature_low = None
-        self._attr_target_temperature_high = None
-
         self._optimistic = config[CONF_OPTIMISTIC]
 
-        if self._topic[CONF_TEMP_STATE_TOPIC] is None:
+        if self._topic[CONF_TEMP_STATE_TOPIC] is None or self._optimistic:
             self._attr_target_temperature = config[CONF_TEMP_INITIAL]
-        if self._topic[CONF_TEMP_LOW_STATE_TOPIC] is None:
+        if self._topic[CONF_TEMP_LOW_STATE_TOPIC] is None or self._optimistic:
             self._attr_target_temperature_low = config[CONF_TEMP_INITIAL]
-        if self._topic[CONF_TEMP_HIGH_STATE_TOPIC] is None:
+        if self._topic[CONF_TEMP_HIGH_STATE_TOPIC] is None or self._optimistic:
             self._attr_target_temperature_high = config[CONF_TEMP_INITIAL]
 
-        if self._topic[CONF_FAN_MODE_STATE_TOPIC] is None:
+        if self._topic[CONF_FAN_MODE_STATE_TOPIC] is None or self._optimistic:
             self._attr_fan_mode = FAN_LOW
-        if self._topic[CONF_SWING_MODE_STATE_TOPIC] is None:
+        if self._topic[CONF_SWING_MODE_STATE_TOPIC] is None or self._optimistic:
             self._attr_swing_mode = SWING_OFF
-        if self._topic[CONF_MODE_STATE_TOPIC] is None:
+        if self._topic[CONF_MODE_STATE_TOPIC] is None or self._optimistic:
             self._attr_hvac_mode = HVACMode.OFF
+        if self._topic[CONF_AUX_STATE_TOPIC] is None or self._optimistic:
+            self._attr_is_aux_heat = False
         self._feature_preset_mode = CONF_PRESET_MODE_COMMAND_TOPIC in config
         if self._feature_preset_mode:
             presets = []
@@ -499,9 +500,6 @@ class MqttClimate(MqttEntity, ClimateEntity):
         self._optimistic_preset_mode = (
             self._optimistic or CONF_PRESET_MODE_STATE_TOPIC not in config
         )
-        self._attr_hvac_action = None
-
-        self._attr_is_aux_heat = False
 
         value_templates: dict[str, Template | None] = {}
         for key in VALUE_TEMPLATE_KEYS:
diff --git a/tests/components/mqtt/test_climate.py b/tests/components/mqtt/test_climate.py
index 67c6e2b4a82..817d0734567 100644
--- a/tests/components/mqtt/test_climate.py
+++ b/tests/components/mqtt/test_climate.py
@@ -258,7 +258,7 @@ async def test_set_operation_optimistic(hass, mqtt_mock_entry_with_yaml_config):
     await mqtt_mock_entry_with_yaml_config()
 
     state = hass.states.get(ENTITY_CLIMATE)
-    assert state.state == "unknown"
+    assert state.state == "off"
 
     await common.async_set_hvac_mode(hass, "cool", ENTITY_CLIMATE)
     state = hass.states.get(ENTITY_CLIMATE)
@@ -351,7 +351,7 @@ async def test_set_fan_mode_optimistic(hass, mqtt_mock_entry_with_yaml_config):
     await mqtt_mock_entry_with_yaml_config()
 
     state = hass.states.get(ENTITY_CLIMATE)
-    assert state.attributes.get("fan_mode") is None
+    assert state.attributes.get("fan_mode") == "low"
 
     await common.async_set_fan_mode(hass, "high", ENTITY_CLIMATE)
     state = hass.states.get(ENTITY_CLIMATE)
@@ -431,7 +431,7 @@ async def test_set_swing_optimistic(hass, mqtt_mock_entry_with_yaml_config):
     await mqtt_mock_entry_with_yaml_config()
 
     state = hass.states.get(ENTITY_CLIMATE)
-    assert state.attributes.get("swing_mode") is None
+    assert state.attributes.get("swing_mode") == "off"
 
     await common.async_set_swing_mode(hass, "on", ENTITY_CLIMATE)
     state = hass.states.get(ENTITY_CLIMATE)
@@ -550,7 +550,7 @@ async def test_set_target_temperature_optimistic(
     await mqtt_mock_entry_with_yaml_config()
 
     state = hass.states.get(ENTITY_CLIMATE)
-    assert state.attributes.get("temperature") is None
+    assert state.attributes.get("temperature") == 21
     await common.async_set_hvac_mode(hass, "heat", ENTITY_CLIMATE)
     await common.async_set_temperature(hass, temperature=17, entity_id=ENTITY_CLIMATE)
     state = hass.states.get(ENTITY_CLIMATE)
@@ -634,8 +634,8 @@ async def test_set_target_temperature_low_high_optimistic(
     await mqtt_mock_entry_with_yaml_config()
 
     state = hass.states.get(ENTITY_CLIMATE)
-    assert state.attributes.get("target_temp_low") is None
-    assert state.attributes.get("target_temp_high") is None
+    assert state.attributes.get("target_temp_low") == 21
+    assert state.attributes.get("target_temp_high") == 21
     await common.async_set_temperature(
         hass, target_temp_low=20, target_temp_high=23, entity_id=ENTITY_CLIMATE
     )