diff --git a/include/config.h b/include/config.h
index a8191d7..c02bdcc 100644
--- a/include/config.h
+++ b/include/config.h
@@ -38,13 +38,13 @@
 // ============================================================================
 #define CLIENT_ID "tanksensor"
 #define DEVICE_VERSION "v1.0.0"
+#define MDNS_HOSTNAME "dusa"
+#define OTA_PORT 80
 
 // ============================================================================
 // ADC Configuration
 // ============================================================================
 #define ADC_RESOLUTION 12              // 12-bit ADC (0-4095)
-#define ADC_MAX 4095
-#define ADC_VREF 3.3f
 
 // ADC reading parameters
 #define ADC_SAMPLES 64                 // Number of samples to average
@@ -63,7 +63,6 @@
 // ============================================================================
 #define READ_INTERVAL_MS 5000          // Read ADC every 5 seconds
 #define PUBLISH_INTERVAL_MS 30000      // Publish to MQTT every 30 seconds
-#define HEARTBEAT_INTERVAL_MS 60000    // Keepalive every 60 seconds
 
 // Connection timeouts
 #define WIFI_CONNECT_TIMEOUT_MS 30000  // WiFi connection timeout
@@ -74,6 +73,9 @@
 #define WIFI_RECONNECT_DELAY_MS 5000   // Delay between WiFi reconnect attempts
 #define MQTT_RECONNECT_DELAY_MS 2000   // Delay between MQTT reconnect attempts
 
+// Watchdog
+#define WDT_TIMEOUT_S 30              // Hardware watchdog timeout (seconds)
+
 // ============================================================================
 // Pin Assignments (XIAO ESP32-S3)
 // ============================================================================
diff --git a/src/main.cpp b/src/main.cpp
index 40226bd..c2c60c6 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -15,6 +15,9 @@
 #include <WiFiClientSecure.h>
 #endif
 #include <ESPmDNS.h>
+#include <WebServer.h>
+#include <Update.h>
+#include <esp_task_wdt.h>
 #include <PubSubClient.h>
 #include <ArduinoJson.h>
 
@@ -34,7 +37,6 @@ struct TankConfig {
 struct TankState {
     int rawADC;            // Raw ADC reading
     int level;             // Level percentage (0-100)
-    int lastPublishedLevel;
     bool registered;
     char topicPath[64];    // W/portalId/tank/N path from registration
     int deviceInstance;
@@ -77,6 +79,8 @@ PubSubClient mqttClient(wifiClient);
 
 TankState tankStates[TANK_COUNT];
 DeviceState deviceState = STATE_INIT;
+WebServer otaServer(OTA_PORT);
+bool otaInitialized = false;
 
 char portalId[32] = "";
 bool allTanksRegistered = false;
@@ -86,7 +90,6 @@ IPAddress mqttServerIP;
 // Timing
 unsigned long lastReadTime = 0;
 unsigned long lastPublishTime = 0;
-unsigned long lastHeartbeatTime = 0;
 unsigned long stateEnteredTime = 0;
 unsigned long lastWiFiAttempt = 0;
 unsigned long lastMQTTAttempt = 0;
@@ -278,6 +281,49 @@ bool resolveMqttServer() {
     return false;
 }
 
+// ============================================================================
+// OTA Functions
+// ============================================================================
+
+void otaSetup() {
+    if (otaInitialized) return;
+
+    MDNS.begin(MDNS_HOSTNAME);
+
+    otaServer.on("/update", HTTP_POST, []() {
+        bool ok = !Update.hasError();
+        otaServer.sendHeader("Connection", "close");
+        otaServer.send(ok ? 200 : 500, "text/plain", ok ? "OK\n" : "FAIL\n");
+        if (ok) {
+            delay(500);
+            ESP.restart();
+        }
+    }, []() {
+        HTTPUpload& upload = otaServer.upload();
+        if (upload.status == UPLOAD_FILE_START) {
+            DEBUG_PRINTF("OTA update: %s\n", upload.filename.c_str());
+            if (!Update.begin(UPDATE_SIZE_UNKNOWN)) {
+                DEBUG_PRINTF("OTA begin failed: %s\n", Update.errorString());
+            }
+        } else if (upload.status == UPLOAD_FILE_WRITE) {
+            esp_task_wdt_reset();
+            if (Update.write(upload.buf, upload.currentSize) != upload.currentSize) {
+                DEBUG_PRINTF("OTA write failed: %s\n", Update.errorString());
+            }
+        } else if (upload.status == UPLOAD_FILE_END) {
+            if (Update.end(true)) {
+                DEBUG_PRINTF("OTA complete: %u bytes\n", upload.totalSize);
+            } else {
+                DEBUG_PRINTF("OTA end failed: %s\n", Update.errorString());
+            }
+        }
+    });
+
+    otaServer.begin();
+    otaInitialized = true;
+    DEBUG_PRINTF("OTA ready: http://%s.local/update\n", MDNS_HOSTNAME);
+}
+
 // ============================================================================
 // MQTT Functions
 // ============================================================================
@@ -472,8 +518,6 @@ void publishTankViaProxy(int tankIndex) {
     
     DEBUG_PRINTF("Publishing %s: %s\n", topic, payload);
     mqttClient.publish(topic, payload);
-    
-    state.lastPublishedLevel = state.level;
 }
 
 void publishAllTanks() {
@@ -507,7 +551,8 @@ void runStateMachine() {
         case STATE_WIFI_CONNECT:
             if (wifiIsConnected()) {
                 DEBUG_PRINTF("WiFi connected, IP: %s\n", WiFi.localIP().toString().c_str());
-                
+                otaSetup();
+
                 // Resolve MQTT server hostname (supports mDNS .local names)
                 if (resolveMqttServer()) {
                     mqttClient.setServer(mqttServerIP, MQTT_PORT);
@@ -570,12 +615,15 @@ void runStateMachine() {
             
         case STATE_RUNNING:
             if (!wifiIsConnected()) {
+                clearRegistration();
                 changeState(STATE_WIFI_CONNECT);
                 break;
             }
-            
+
             if (!mqttClient.connected()) {
                 clearRegistration();
+                resolveMqttServer();
+                mqttClient.setServer(mqttServerIP, MQTT_PORT);
                 changeState(STATE_MQTT_CONNECT);
                 break;
             }
@@ -679,7 +727,6 @@ void setup() {
     for (int i = 0; i < TANK_COUNT; i++) {
         tankStates[i].rawADC = 0;
         tankStates[i].level = 0;
-        tankStates[i].lastPublishedLevel = -1;
         tankStates[i].registered = false;
         tankStates[i].topicPath[0] = '\0';
         tankStates[i].deviceInstance = 0;
@@ -689,13 +736,24 @@ void setup() {
     adcSetup();
     wifiSetup();
     mqttSetup();
-    
+
+    // Hardware watchdog — resets device if loop() stalls
+    esp_task_wdt_config_t wdtConfig = {
+        .timeout_ms = WDT_TIMEOUT_S * 1000,
+        .idle_core_mask = 0,
+        .trigger_panic = true,
+    };
+    esp_task_wdt_reconfigure(&wdtConfig);
+    esp_task_wdt_add(NULL);
+
     DEBUG_PRINTLN("Setup complete, starting state machine");
 }
 
 void loop() {
     unsigned long now = millis();
-    
+    esp_task_wdt_reset();
+    otaServer.handleClient();
+
     // Always process MQTT messages
     if (mqttClient.connected()) {
         mqttClient.loop();