diff --git a/front/plugins/_publisher_mqtt/mqtt.py b/front/plugins/_publisher_mqtt/mqtt.py
index 7727ca4f..08ece315 100755
--- a/front/plugins/_publisher_mqtt/mqtt.py
+++ b/front/plugins/_publisher_mqtt/mqtt.py
@@ -3,7 +3,6 @@
 import json
 import os
 import sys
-from datetime import datetime
 import time
 import re
 import paho.mqtt.client as mqtt
@@ -26,7 +25,7 @@ from logger import mylog, Logger  # noqa: E402 [flake8 lint suppression]
 from helper import get_setting_value, bytes_to_string, \
     sanitize_string, normalize_string  # noqa: E402 [flake8 lint suppression]
 from database import DB, get_device_stats  # noqa: E402 [flake8 lint suppression]
-from utils.datetime_utils import timeNowUTC  # noqa: E402 [flake8 lint suppression]
+from utils.datetime_utils import timeNowUTC, format_date_iso  # noqa: E402 [flake8 lint suppression]
 from models.notification_instance import NotificationInstance  # noqa: E402 [flake8 lint suppression]
 
 # Make sure the TIMEZONE for logging is correct
@@ -504,8 +503,8 @@ def mqtt_start(db):
                 "vendor": sanitize_string(device["devVendor"]),
                 "mac_address": str(device["devMac"]),
                 "model": devDisplayName,
-                "last_connection": prepTimeStamp(str(device["devLastConnection"])),
-                "first_connection": prepTimeStamp(str(device["devFirstConnection"])),
+                "last_connection": format_date_iso(str(device["devLastConnection"])),
+                "first_connection": format_date_iso(str(device["devFirstConnection"])),
                 "sync_node": device["devSyncHubNode"],
                 "group": device["devGroup"],
                 "location": device["devLocation"],
@@ -617,26 +616,6 @@ def to_binary_sensor(input):
     return "OFF"
 
 
-#  -------------------------------------
-# Convert to format that is interpretable by Home Assistant
-def prepTimeStamp(datetime_str):
-    try:
-        # Attempt to parse the input string to ensure it's a valid datetime
-        parsed_datetime = datetime.fromisoformat(datetime_str)
-
-        # If the parsed datetime is naive (i.e., does not contain timezone info), add UTC timezone
-        if parsed_datetime.tzinfo is None:
-            parsed_datetime = conf.tz.localize(parsed_datetime)
-
-    except ValueError:
-        mylog('verbose', [f"[{pluginName}]  Timestamp conversion failed of string '{datetime_str}'"])
-        # Use the current time if the input format is invalid
-        parsed_datetime = timeNowUTC(as_string=False)
-
-    # Convert to the required format with 'T' between date and time and ensure the timezone is included
-    return parsed_datetime.isoformat()  # This will include the timezone offset
-
-
 #  -------------INIT---------------------
 if __name__ == '__main__':
     sys.exit(main())
diff --git a/test/server/test_datetime_utils.py b/test/server/test_datetime_utils.py
index 0161e765..afd0ccd5 100644
--- a/test/server/test_datetime_utils.py
+++ b/test/server/test_datetime_utils.py
@@ -15,7 +15,7 @@ import pytest
 INSTALL_PATH = os.getenv('NETALERTX_APP', '/app')
 sys.path.extend([f"{INSTALL_PATH}/front/plugins", f"{INSTALL_PATH}/server"])
 
-from utils.datetime_utils import timeNowUTC, DATETIME_PATTERN  # noqa: E402
+from utils.datetime_utils import timeNowUTC, format_date_iso, DATETIME_PATTERN  # noqa: E402
 
 
 class TestTimeNowUTC:
@@ -104,3 +104,52 @@ class TestTimeNowUTC:
         t2 = datetime.datetime.strptime(t2_str, DATETIME_PATTERN)
 
         assert t2 >= t1
+
+
+class TestFormatDateIso:
+    """
+    Regression tests for format_date_iso().
+
+    Root cause being guarded: DB timestamps are stored as naive UTC strings
+    (e.g. '2026-04-04 08:54:00'). The old prepTimeStamp() called
+    conf.tz.localize() which LABELS the naive value with the local TZ offset
+    instead of CONVERTING it. This made '08:54 UTC' become '08:54+02:00',
+    telling Home Assistant the event happened at 06:54 UTC — 2 hours too early.
+
+    format_date_iso() correctly replaces(tzinfo=UTC) first, then converts.
+    """
+
+    def test_naive_utc_string_gets_utc_tzinfo(self):
+        """A naive DB timestamp must be interpreted as UTC, not local time."""
+        result = format_date_iso("2026-04-04 08:54:00")
+        assert result is not None
+        # Must contain a TZ offset ('+' or 'Z'), not be naive
+        assert "+" in result or result.endswith("Z"), \
+            f"Expected timezone in ISO output, got: {result}"
+
+    def test_naive_utc_string_offset_reflects_utc_source(self):
+        """
+        The UTC instant must be preserved.  Whatever the local offset, the
+        calendar moment encoded in the ISO string must equal 08:54 UTC.
+        """
+        result = format_date_iso("2026-04-04 08:54:00")
+        parsed = datetime.datetime.fromisoformat(result)
+        # Normalise to UTC for the assertion
+        utc_parsed = parsed.astimezone(datetime.UTC)
+        assert utc_parsed.hour == 8
+        assert utc_parsed.minute == 54
+
+    def test_empty_string_returns_none(self):
+        """format_date_iso('') must return None, not raise."""
+        assert format_date_iso("") is None
+
+    def test_none_returns_none(self):
+        """format_date_iso(None) must return None, not raise."""
+        assert format_date_iso(None) is None
+
+    def test_output_is_valid_iso8601(self):
+        """Output must be parseable by datetime.fromisoformat()."""
+        result = format_date_iso("2026-01-15 12:00:00")
+        assert result is not None
+        # Should not raise
+        datetime.datetime.fromisoformat(result)