diff --git a/android/app/src/main/assets/firmware/server/firmware.bin b/android/app/src/main/assets/firmware/server/firmware.bin
index 3bfedd2..0e91add 100644
Binary files a/android/app/src/main/assets/firmware/server/firmware.bin and b/android/app/src/main/assets/firmware/server/firmware.bin differ
diff --git a/android/app/src/main/java/nl/eddydevink/sylda/BleRelayManager.kt b/android/app/src/main/java/nl/eddydevink/sylda/BleRelayManager.kt
index 29ceeae..cf5a98e 100644
--- a/android/app/src/main/java/nl/eddydevink/sylda/BleRelayManager.kt
+++ b/android/app/src/main/java/nl/eddydevink/sylda/BleRelayManager.kt
@@ -373,7 +373,8 @@ class BleRelayManager(
                     ((value[3].toInt() and 0xFF) shl 8) or
                     (value[4].toInt() and 0xFF)
                 } else 0
-                Log.d(TAG, "OTA notify: status=$status seq=$seq")
+                val statusName = when (status) { 0x00 -> "ACK"; 0x01 -> "NAK"; 0x10 -> "COMPLETE"; 0x11 -> "ERROR"; else -> "UNKNOWN(0x${status.toString(16)})" }
+                Log.d(TAG, "OTA notify: status=$statusName seq=$seq raw=${value.joinToString("") { "%02X".format(it) }}")
                 handler.post { otaNotifyCallback?.onOtaNotify(status, seq) }
             }
         }
diff --git a/android/app/src/main/java/nl/eddydevink/sylda/OtaManager.kt b/android/app/src/main/java/nl/eddydevink/sylda/OtaManager.kt
index 993ad07..0b2d3c9 100644
--- a/android/app/src/main/java/nl/eddydevink/sylda/OtaManager.kt
+++ b/android/app/src/main/java/nl/eddydevink/sylda/OtaManager.kt
@@ -65,6 +65,7 @@ class OtaManager(
 
         val notifyCallback = object : BleRelayManager.OtaNotifyCallback {
             override fun onOtaNotify(status: Int, seq: Int) {
+                Log.d(TAG, "OTA notify received: status=0x${status.toString(16)} seq=$seq (0x00=ACK, 0x01=NAK, 0x10=COMPLETE, 0x11=ERROR)")
                 when (status) {
                     0x00 -> chunkAckReceived = true
                     0x01 -> chunkNakReceived = true
@@ -163,7 +164,9 @@ class OtaManager(
             withContext(Dispatchers.Main) { callback.onProgress(99, "Hash verifiëren...") }
 
             finalStatusReceived = false
-            relayManager.sendOtaData(sha256)
+            Log.d(TAG, "Sending SHA256 hash (${sha256.size} bytes) to ESP")
+            val shaSent = relayManager.sendOtaData(sha256)
+            Log.d(TAG, "SHA256 write result: $shaSent")
 
             try {
                 withTimeout(OTA_FINAL_TIMEOUT_MS) {
@@ -173,12 +176,17 @@ class OtaManager(
                     }
                 }
             } catch (_: kotlinx.coroutines.TimeoutCancellationException) {
-                Log.w(TAG, "Timeout waiting for final OTA status")
+                Log.w(TAG, "Timeout waiting for final OTA status after SHA256")
             }
 
+            Log.d(TAG, "Final status: received=$finalStatusReceived status=$finalStatus (0x10=COMPLETE, 0x11=ERROR)")
+
             relayManager.setOtaNotifyCallback(null)
 
             if (finalStatus == 0x10) {
+                Log.d(TAG, "ESP confirmed SHA256 OK, sending 0xFF reboot confirmation")
+                val confirmSent = relayManager.sendOtaData(byteArrayOf(0xFF.toByte()))
+                Log.d(TAG, "0xFF write result: $confirmSent")
                 withContext(Dispatchers.Main) {
                     callback.onProgress(100, "Herstart...")
                     callback.onComplete()
diff --git a/src/client.cpp b/src/client.cpp
index 5053873..2f53914 100644
--- a/src/client.cpp
+++ b/src/client.cpp
@@ -424,7 +424,7 @@ void loop() {
     }
 
     static uint32_t heartbeat = 0;
-    if (millis() - heartbeat > 5000) {
+    if (millis() - heartbeat > 60000) {
         Serial.printf("[heartbeat] t1=%s t2=%s btn=%s r1=%s r2=%s connected=%s\n",
             t1Active ? "YES" : "no",
             t2Active ? "YES" : "no",
diff --git a/src/main.cpp b/src/main.cpp
index faa8f80..75a67ef 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -63,6 +63,11 @@ uint32_t otaWritten = 0;
 uint8_t otaExpectedSha[32];
 mbedtls_sha256_context otaShaCtx;
 bool otaShaStarted = false;
+bool otaReady = false;
+bool otaEnded = false;
+bool otaConfirmed = false;
+uint32_t otaEndedAt = 0;
+#define OTA_CONFIRM_TIMEOUT_MS 10000
 
 uint8_t hmacKey[HMAC_KEY_LEN];
 uint8_t deviceUuid[ESP_UUID_LEN];
@@ -183,6 +188,9 @@ static void otaReset() {
     otaPartition = nullptr;
     otaExpectedSize = 0;
     otaWritten = 0;
+    otaReady = false;
+    otaEnded = false;
+    otaConfirmed = false;
     if (otaShaStarted) {
         mbedtls_sha256_free(&otaShaCtx);
         otaShaStarted = false;
@@ -258,36 +266,40 @@ class OtaCharacteristicCallbacks : public NimBLECharacteristicCallbacks {
             mbedtls_sha256_finish_ret(&otaShaCtx, computedSha);
             mbedtls_sha256_free(&otaShaCtx);
             otaShaStarted = false;
-            esp_err_t err = esp_ota_end(otaHandle);
-            if (err != ESP_OK) {
-                Serial.printf("OTA: end failed (%d)\n", err);
-                otaReset();
-                sendOtaNotify(pChar, OTA_STATUS_ERROR, 0);
-                return;
-            }
+
+            Serial.printf("OTA: SHA256 verify — written=%lu expected=%lu\n", otaWritten, otaExpectedSize);
             if (memcmp(computedSha, otaExpectedSha, 32) != 0) {
                 Serial.println("OTA: SHA256 mismatch — aborting");
+                esp_ota_abort(otaHandle);
                 otaReset();
                 sendOtaNotify(pChar, OTA_STATUS_ERROR, 0);
                 return;
             }
-            err = esp_ota_set_boot_partition(otaPartition);
-            if (err != ESP_OK) {
-                Serial.printf("OTA: set boot partition failed (%d)\n", err);
-                otaReset();
-                sendOtaNotify(pChar, OTA_STATUS_ERROR, 0);
-                return;
-            }
-            leds[0] = CRGB::Green;
-            FastLED.show();
+
+            Serial.println("OTA: SHA256 OK, setting otaReady=true, sending COMPLETE notify");
+            otaReady = true;
             sendOtaNotify(pChar, OTA_STATUS_COMPLETE, 0);
-            Serial.println("OTA: SHA256 OK, rebooting...");
-            delay(500);
-            esp_restart();
+            Serial.printf("OTA: COMPLETE notify sent, otaReady=%d, otaConfirmed=%d, otaInProgress=%d\n",
+                          otaReady, otaConfirmed, otaInProgress);
             return;
         }
 
-        if (!otaInProgress) return;
+        if (!otaInProgress) {
+            Serial.printf("OTA: write ignored — otaInProgress=false (len=%d, data0=0x%02X)\n", len, data[0]);
+            return;
+        }
+
+        if (len == 1 && data[0] == 0xFF) {
+            Serial.printf("OTA: 0xFF received — otaReady=%d, otaEnded=%d, otaConfirmed=%d, otaInProgress=%d\n",
+                          otaReady, otaEnded, otaConfirmed, otaInProgress);
+            if (!otaEnded) {
+                Serial.println("OTA: 0xFF IGNORED — otaEnded is false (esp_ota_end not yet called or failed)");
+                return;
+            }
+            Serial.println("OTA: 0xFF confirm accepted, setting otaConfirmed=true");
+            otaConfirmed = true;
+            return;
+        }
 
         if (data[0] < 0x10) {
             uint32_t seq = ((uint32_t)data[0] << 24) | ((uint32_t)data[1] << 16) |
@@ -521,6 +533,46 @@ void loop() {
         }
     }
 
+    if (otaReady) {
+        Serial.printf("OTA: loop() processing otaReady — otaWritten=%lu, otaExpectedSize=%lu\n",
+                      otaWritten, otaExpectedSize);
+        esp_err_t err = esp_ota_end(otaHandle);
+        if (err != ESP_OK) {
+            Serial.printf("OTA: esp_ota_end failed (%d) — aborting\n", err);
+            otaReset();
+        } else {
+            Serial.println("OTA: esp_ota_end OK, setting otaEnded=true, waiting for 0xFF confirm");
+            otaEnded = true;
+            otaEndedAt = millis();
+            leds[0] = CRGB::Yellow;
+            FastLED.show();
+        }
+        otaReady = false;
+        Serial.printf("OTA: otaReady cleared — otaReady=%d, otaEnded=%d, otaConfirmed=%d, otaInProgress=%d\n",
+                      otaReady, otaEnded, otaConfirmed, otaInProgress);
+    }
+
+    if (otaEnded && !otaConfirmed && (millis() - otaEndedAt > OTA_CONFIRM_TIMEOUT_MS)) {
+        Serial.printf("OTA: 0xFF confirm timeout (%lu ms) — discarding update, resuming normal operation\n",
+                      millis() - otaEndedAt);
+        otaReset();
+    }
+
+    if (otaConfirmed) {
+        Serial.println("OTA: otaConfirmed=true, setting boot partition");
+        esp_err_t err = esp_ota_set_boot_partition(otaPartition);
+        if (err != ESP_OK) {
+            Serial.printf("OTA: set boot partition failed (%d)\n", err);
+        } else {
+            leds[0] = CRGB::Green;
+            FastLED.show();
+            Serial.println("OTA: done, rebooting...");
+            delay(500);
+            esp_restart();
+        }
+        otaReset();
+    }
+
     static bool t1Stable = false;
     static bool t2Stable = false;
     static bool btnStable = false;
@@ -574,7 +626,7 @@ void loop() {
     }
 
     static uint32_t heartbeat = 0;
-    if (!otaInProgress && millis() - heartbeat > 5000) {
+    if (!otaInProgress && millis() - heartbeat > 60000) {
         bool anyBle1 = (connActive[0] && bleRelay1[0]) || (connActive[1] && bleRelay1[1]);
         bool anyBle2 = (connActive[0] && bleRelay2[0]) || (connActive[1] && bleRelay2[1]);
         Serial.printf("[heartbeat] R1=%s R2=%s t1=%s t2=%s btn=%s ble1=%s ble2=%s clients=%d\n",
diff --git a/version.txt b/version.txt
index 9f9522d..cf5c08b 100644
--- a/version.txt
+++ b/version.txt
@@ -1,2 +1,2 @@
-server=8
+server=15
 client=1