diff --git a/psa_car_controller/psacc/repository/config_repository.py b/psa_car_controller/psacc/repository/config_repository.py
index 473784a..ed9a64e 100644
--- a/psa_car_controller/psacc/repository/config_repository.py
+++ b/psa_car_controller/psacc/repository/config_repository.py
@@ -50,12 +50,12 @@ def replace_key_underscore_by_space(obj, key):
     return new_obj
 
 
-class Hour:
-    reg = re.compile(r"([0-9]{1,2})h([0-9]{1,2})")
+HOUR_REGEX = re.compile(r"([0-9]{1,2})h([0-9]{1,2})")
 
-    def __init__(self, hours: int, minutes: int):
-        self.hours = hours
-        self.minutes = minutes
+
+class Hour(str):
+    hours: int
+    minutes: int
 
     @classmethod
     def __get_validators__(cls):
@@ -68,10 +68,13 @@ class Hour:
         if len(v) == 0:
             return None
 
-        m = Hour.reg.fullmatch(v.lower())
+        m = HOUR_REGEX.fullmatch(v.lower())
         if not m:
             raise ValueError('invalid hour format')
-        return cls(int(m.group(1)), int(m.group(2)))
+        hour = cls(v)
+        hour.hours = int(m.group(1))
+        hour.minutes = int(m.group(2))
+        return hour
 
     def __repr__(self):
         return '{}h{}'.format(self.hours, self.minutes)
@@ -188,6 +191,8 @@ class ConfigRepository(BaseModel):
     def write_config(self, name=None):
         if name is None:
             name = CONFIG_FILENAME
+        self.validate(self)
+        ConfigRepository(**self.dict())  # validate property before write
         config_to_write = ConfigRepository.get_default_config()
         self.config_dto_to_config_file(config_to_write)
         self._write(name, config_to_write)
diff --git a/tests/test_config.py b/tests/test_config.py
index f3d9d38..2849d52 100644
--- a/tests/test_config.py
+++ b/tests/test_config.py
@@ -1,3 +1,4 @@
+import json
 import os
 import unittest
 from configparser import ConfigParser
@@ -33,8 +34,9 @@ night hour end = 4h42
         self.assertEqual(config_written["General"]["currency"].value, "€")
         self.assertEqual(config_written["Electricity config"]["day price"].value, 42)
         self.assertEqual(config_written["Electricity config"]["night price"].value, 0.1)
-        self.assertEqual(str(config_written["Electricity config"]["night hour start"].value), "1h0")
+        self.assertEqual(str(config_written["Electricity config"]["night hour start"].value), "1h00")
         self.assertEqual(str(config_written["Electricity config"]["night hour end"].value), "4h42")
+        conf.json()
 
     def test_read_non_existent_config(self):
         from psa_car_controller.psacc.repository.config_repository import ConfigRepository
@@ -46,6 +48,12 @@ night hour end = 4h42
         expected_result = ConfigRepository.config_file_to_dto(ConfigRepository.get_default_config())
         self.assertEqual(result, expected_result)
 
+    @patch("psa_car_controller.psacc.repository.config_repository.ConfigRepository._write")
+    def test_read_invalid_hour(self, mock_write):
+        conf = ConfigRepository.config_file_to_dto(ConfigRepository.get_default_config())
+        conf.Electricity_config.night_hour_start = "200"
+        self.assertRaises(ValueError, lambda: conf.write_config())
+
 
 if __name__ == '__main__':
     my_logger(handler_level=os.environ.get("DEBUG_LEVEL", 20))