diff --git a/oin_thermostat/mqtt.py b/oin_thermostat/mqtt.py
index c20dc86..934e002 100644
--- a/oin_thermostat/mqtt.py
+++ b/oin_thermostat/mqtt.py
@@ -1,5 +1,8 @@
 import json
 import logging
+import sys
+from collections.abc import Callable
+from typing import Any
 
 import paho.mqtt.client as mqtt
 
@@ -14,7 +17,7 @@ class HAClient:
         self,
         entity: str,
         secondary_entities: list[str] = [],
-        mqtt_config: dict = dict(),
+        mqtt_config: dict[str, str] = dict(),
     ) -> None:
         self.entity = entity
         self.secondary_entities = secondary_entities
@@ -54,34 +57,48 @@ class HAClient:
 
         host = self.config.get("host")
         port = self.config.get("port", 1883)
-        logger.debug(f"Connecting to <{host}> on port <{port}>")
+        logger.debug(f"Connecting to <{host}> on port <{port}>.")
         self.client.connect(host, port)
 
         self.subscribe(entity_topic(self.entity), self.state_update)
-        for entity in self.secondary_entities:
-            self.subscribe(entity_topic(entity, "state"), self.secondary_state_update)
+        self.subscribe(
+            [entity_topic(entity) for entity in self.secondary_entities],
+            self.secondary_state_update,
+        )
 
         self.publish("homeassistant/device/oin/config", self.ha_options, retain=True)
         self.client.publish(self.availability_topic, "online", retain=True)
 
-    def publish(self, topic, data, **kwargs):
+    def publish(self, topic: str, data: Any, **kwargs) -> mqtt.MQTTMessageInfo:
         logger.debug(f"Sending message on topic <{topic}>: {json.dumps(data)}")
-        self.client.publish(topic, json.dumps(data), **kwargs)
+        return self.client.publish(topic, json.dumps(data), **kwargs)
 
-    def subscribe(self, topic, callback):
-        logger.debug(f"Subscribe to <{topic}>")
-        self.client.subscribe(topic)
-        self.client.message_callback_add(topic, callback)
+    def subscribe(self, topic: str | list[str], callback: Callable) -> None:
+        logger.debug(f"Subscribing to <{topic}>.")
 
-    def unsubscribe(self, topic):
-        logger.debug(f"Unsubscribe from <{topic}>")
-        self.client.unsubscribe(topic)
+        match topic:
+            case str():
+                self.client.message_callback_add(topic, callback)
+                code, _ = self.client.subscribe(topic)
+            case list():
+                for top in topic:
+                    self.client.message_callback_add(top, callback)
+                code, _ = self.client.subscribe([(top, 0) for top in topic])
 
-    def loop(self):
-        logger.info("Starting MQTT client loop")
-        self.client.loop_forever()
+        if code != 0:
+            logger.error(f"Failed subscribing to topic <{topic}> with code <{code}>.")
+            sys.exit(1)
 
-    def state_update(self, client: mqtt.Client, userdata, message: mqtt.MQTTMessage):
+    def loop(self) -> mqtt.MQTTErrorCode:
+        logger.info("Starting MQTT client loop.")
+        code = self.client.loop_forever(retry_first_connection=True)
+
+        if code != 0:
+            logger.error("MQTT client loop failed with code <{code}>.")
+
+    def state_update(
+        self, client: mqtt.Client, userdata: Any, message: mqtt.MQTTMessage
+    ) -> None:
         logger.debug(f"Message received on topic <{message.topic}>: {message.payload}.")
 
         subtopic = message.topic.rsplit("/", maxsplit=1)[1]
@@ -109,8 +126,8 @@ class HAClient:
                         self.selector.switch = False
 
     def secondary_state_update(
-        self, client: mqtt.Client, userdata, message: mqtt.MQTTMessage
-    ):
+        self, client: mqtt.Client, userdata: Any, message: mqtt.MQTTMessage
+    ) -> None:
         logger.debug(f"Message received on topic <{message.topic}>: {message.payload}.")
 
         _, grp, ent, subtopic = message.topic.split("/")
@@ -119,14 +136,14 @@ class HAClient:
         if subtopic == "state":
             self.screen.secondary |= {idx: message.payload.decode()}
 
-    def send_data(self, data):
-        self.publish(self.state_topic, data)
+    def send_data(self, data: Any) -> mqtt.MQTTMessageInfo:
+        return self.publish(self.state_topic, data)
 
 
-def parse(message):
+def parse(message: mqtt.MQTTMessage) -> Any:
     return json.loads(message.payload.decode())
 
 
-def entity_topic(entity, subtopic="#"):
+def entity_topic(entity: str, subtopic: str = "#") -> str:
     topic = entity.replace(".", "/")
     return f"homeassistant/{topic}/{subtopic}"