diff --git a/src/knx/group_object.cpp b/src/knx/group_object.cpp
index 6898ba5b..cf3ad24e 100644
--- a/src/knx/group_object.cpp
+++ b/src/knx/group_object.cpp
@@ -12,7 +12,8 @@ GroupObjectTableObject* GroupObject::_table = 0;
 GroupObject::GroupObject()
 {
     _data = 0;
-    _commFlag = Uninitialized;
+    _commFlagEx.uninitialized = true;
+    _commFlagEx.commFlag = Uninitialized;
     _dataLength = 0;
 #ifndef SMALL_GROUPOBJECT
     _updateHandler = 0;
@@ -22,7 +23,7 @@ GroupObject::GroupObject()
 GroupObject::GroupObject(const GroupObject& other)
 {
     _data = new uint8_t[other._dataLength];
-    _commFlag = other._commFlag;
+    _commFlagEx = other._commFlagEx;
     _dataLength = other._dataLength;
     _asap = other._asap;
 #ifndef SMALL_GROUPOBJECT
@@ -75,7 +76,7 @@ bool GroupObject::readEnable()
         return false;
 
     // we forbid reading of new (uninitialized) go
-    if (_commFlag == Uninitialized)
+    if (_commFlagEx.uninitialized)
         return false;
 
     return bitRead(ntohs(_table->_tableData[_asap]), 11) > 0;
@@ -157,22 +158,29 @@ size_t GroupObject::asapValueSize(uint8_t code)
 
 ComFlag GroupObject::commFlag()
 {
-    return _commFlag;
+    return _commFlagEx.commFlag;
 }
 
 void GroupObject::commFlag(ComFlag value)
 {
-    _commFlag = value;
+    _commFlagEx.commFlag = value;
+    if (value == WriteRequest || value == Updated || value == Ok)
+        _commFlagEx.uninitialized = false;
+}
+
+bool GroupObject::initialized()
+{
+    return !_commFlagEx.uninitialized;
 }
 
 void GroupObject::requestObjectRead()
 {
-    _commFlag = ReadRequest;
+    _commFlagEx.commFlag = ReadRequest;
 }
 
 void GroupObject::objectWritten()
 {
-    _commFlag = WriteRequest;
+    _commFlagEx.commFlag = WriteRequest;
 }
 
 size_t GroupObject::valueSize()
@@ -274,8 +282,11 @@ void GroupObject::valueNoSend(const KNXValue& value)
 
 void GroupObject::valueNoSend(const KNXValue& value, const Dpt& type)
 {
-    if (_commFlag == Uninitialized)
-        _commFlag = Ok;
+    if (_commFlagEx.uninitialized)
+    {
+        _commFlagEx.commFlag = Ok;
+        _commFlagEx.uninitialized = false;
+    }
 
     KNX_Encode_Value(value, _data, _dataLength, type);
 }
diff --git a/src/knx/group_object.h b/src/knx/group_object.h
index 88ce274f..cf46307a 100644
--- a/src/knx/group_object.h
+++ b/src/knx/group_object.h
@@ -7,7 +7,7 @@
 
 class GroupObjectTableObject;
 
-enum ComFlag
+enum ComFlag : uint8_t
 {
     Updated = 0,      //!< Group object was updated
     ReadRequest = 1,  //!< Read was requested but was not processed
@@ -18,6 +18,16 @@ enum ComFlag
     Uninitialized = 6 //!< uninitialized Group Object, its value is not valid
 };
 
+// extended ComFlag: Uninitialized it not handled correctly as ComFlag
+// it might be in state Transmitting during a ReadRequest on startup while value is still not valid
+// we use MSB to store Uninitialized and keep the size of GroupObject the same saving memory ressources
+// the old Uninitialized handling is still there for compatibility reasons.
+struct ComFlagEx
+{
+    bool uninitialized : 1;
+    ComFlag commFlag : 7;
+};
+
 class GroupObject;
 
 #ifndef HAS_FUNCTIONAL
@@ -96,6 +106,11 @@ class GroupObject
      */
     void commFlag(ComFlag value);
 
+    /**
+     * Check if the group object contains a valid value assigned from bus or from application program
+     */
+    bool initialized();
+
     /**
     * Request the read of a communication object. Calling this function triggers the
     * sending of a read-group-value telegram, to read the value of the communication
@@ -236,7 +251,7 @@ class GroupObject
     size_t asapValueSize(uint8_t code);
     size_t goSize();
     uint16_t _asap = 0;
-    ComFlag _commFlag = Uninitialized;
+    ComFlagEx _commFlagEx;
     uint8_t* _data = 0;
     uint8_t _dataLength = 0;
 #ifndef SMALL_GROUPOBJECT