diff --git a/cura/Settings/MachineManager.py b/cura/Settings/MachineManager.py
index 9619329e59..b69d91c0d4 100755
--- a/cura/Settings/MachineManager.py
+++ b/cura/Settings/MachineManager.py
@@ -1220,6 +1220,14 @@ class MachineManager(QObject):
                 for container in hidden_containers:
                     container.setMetaDataEntry("connect_group_name", group_name)
 
+    ##  This method checks if there is an instance connected to the given network_key
+    def existNetworkInstances(self, network_key: str) -> bool:
+        metadata_filter = {"um_network_key": network_key}
+        containers = ContainerRegistry.getInstance().findContainerStacks(type = "machine", **metadata_filter)
+        if containers:
+            return True
+        return False
+
     @pyqtSlot("QVariant")
     def setGlobalVariant(self, container_node):
         self.blurSettings.emit()
diff --git a/plugins/UM3NetworkPrinting/DiscoverUM3Action.py b/plugins/UM3NetworkPrinting/DiscoverUM3Action.py
index 76e8721fdd..0b8d6e9f53 100644
--- a/plugins/UM3NetworkPrinting/DiscoverUM3Action.py
+++ b/plugins/UM3NetworkPrinting/DiscoverUM3Action.py
@@ -147,6 +147,10 @@ class DiscoverUM3Action(MachineAction):
 
         return ""
 
+    @pyqtSlot(str, result = bool)
+    def existsKey(self, key) -> bool:
+        return Application.getInstance().getMachineManager().existNetworkInstances(network_key = key)
+
     @pyqtSlot()
     def loadConfigurationFromPrinter(self):
         machine_manager = Application.getInstance().getMachineManager()
diff --git a/plugins/UM3NetworkPrinting/DiscoverUM3Action.qml b/plugins/UM3NetworkPrinting/DiscoverUM3Action.qml
index 079e5dcdd3..e7df22b546 100644
--- a/plugins/UM3NetworkPrinting/DiscoverUM3Action.qml
+++ b/plugins/UM3NetworkPrinting/DiscoverUM3Action.qml
@@ -5,6 +5,7 @@ import QtQuick 2.2
 import QtQuick.Controls 1.1
 import QtQuick.Layouts 1.1
 import QtQuick.Window 2.1
+import QtQuick.Dialogs 1.2
 
 Cura.MachineAction
 {
@@ -33,15 +34,34 @@ Cura.MachineAction
         {
             var printerKey = base.selectedDevice.key
             var printerName = base.selectedDevice.name  // TODO To change when the groups have a name
-            if(manager.getStoredKey() != printerKey)
+            if (manager.getStoredKey() != printerKey)
             {
-                manager.setKey(printerKey)
-                manager.setGroupName(printerName)   // TODO To change when the groups have a name
-                completed()
+                // Check if there is another instance with the same key
+                if (!manager.existsKey(printerKey))
+                {
+                    manager.setKey(printerKey)
+                    manager.setGroupName(printerName)   // TODO To change when the groups have a name
+                    completed()
+                }
+                else
+                {
+                    existingConnectionDialog.open()
+                }
             }
         }
     }
 
+    MessageDialog
+    {
+        id: existingConnectionDialog
+        title: catalog.i18nc("@window:title", "Existing Connection")
+        icon: StandardIcon.Information
+        text: catalog.i18nc("@message:text", "There is an instance already connected to this group")
+        detailedText: catalog.i18nc("@message:description", "You can't connect two instances to the same group. Please use the other instance or connect to another group.")
+        standardButtons: StandardButton.Ok
+        modality: Qt.ApplicationModal
+    }
+
     Column
     {
         anchors.fill: parent;