diff --git a/DiscoverUM3Action.qml b/DiscoverUM3Action.qml
index 0cd4ba0481..4daeaa1c37 100644
--- a/DiscoverUM3Action.qml
+++ b/DiscoverUM3Action.qml
@@ -11,6 +11,7 @@ Cura.MachineAction
     id: base
     anchors.fill: parent;
     property var selectedPrinter: null
+    property bool completeProperties: true
     property var connectingToPrinter: null
 
     Connections
@@ -84,7 +85,7 @@ Cura.MachineAction
             {
                 id: editButton
                 text: catalog.i18nc("@action:button", "Edit")
-                enabled: base.selectedPrinter && base.selectedPrinter.getKey().substr(0,7) =="manual:"
+                enabled: base.selectedPrinter != null && (base.selectedPrinter.getKey().substr(0,7) =="manual:")
                 onClicked:
                 {
                     manualPrinterDialog.showDialog(base.selectedPrinter.getKey(), base.selectedPrinter.ipAddress);
@@ -95,7 +96,7 @@ Cura.MachineAction
             {
                 id: removeButton
                 text: catalog.i18nc("@action:button", "Remove")
-                enabled: base.selectedPrinter && base.selectedPrinter.getKey().substr(0,7) =="manual:"
+                enabled: base.selectedPrinter != null && (base.selectedPrinter.getKey().substr(0,7) =="manual:")
                 onClicked: manager.removeManualPrinter(base.selectedPrinter.getKey(), base.selectedPrinter.ipAddress)
             }
 
@@ -150,7 +151,12 @@ Cura.MachineAction
                         }
                         width: parent.width
                         currentIndex: -1
-                        onCurrentIndexChanged: base.selectedPrinter = listview.model[currentIndex]
+                        onCurrentIndexChanged:
+                        {
+                            base.selectedPrinter = listview.model[currentIndex];
+                            // Only allow connecting if the printer has responded to API query since the last refresh
+                            base.completeProperties = base.selectedPrinter != null && (base.selectedPrinter.firmwareVersion != "");
+                        }
                         Component.onCompleted: manager.startDiscovery()
                         delegate: Rectangle
                         {
@@ -252,7 +258,7 @@ Cura.MachineAction
                 Button
                 {
                     text: catalog.i18nc("@action:button", "Connect")
-                    enabled: base.selectedPrinter ? true : false
+                    enabled: (base.selectedPrinter && base.completeProperties) ? true : false
                     onClicked: connectToPrinter()
                 }
             }
diff --git a/NetworkPrinterOutputDevicePlugin.py b/NetworkPrinterOutputDevicePlugin.py
index 96c43d5d0d..4843ab8975 100644
--- a/NetworkPrinterOutputDevicePlugin.py
+++ b/NetworkPrinterOutputDevicePlugin.py
@@ -63,7 +63,8 @@ class NetworkPrinterOutputDevicePlugin(OutputDevicePlugin):
 
         # Look for manual instances from preference
         for address in self._manual_instances:
-            self.addManualPrinter(address)
+            if address:
+                self.addManualPrinter(address)
 
     def addManualPrinter(self, address):
         if address not in self._manual_instances:
@@ -72,17 +73,13 @@ class NetworkPrinterOutputDevicePlugin(OutputDevicePlugin):
 
         name = address
         instance_name = "manual:%s" % address
-        properties = { b"name": name.encode("UTF-8") }
+        properties = { b"name": name.encode("UTF-8"), b"incomplete": True }
 
         if instance_name not in self._printers:
             # Add a preliminary printer instance
             self.addPrinter(instance_name, address, properties)
 
-        # Check if a printer exists at this address
-        # If a printer responds, it will replace the preliminary printer created above
-        url = QUrl("http://" + address + self._api_prefix + "system")
-        name_request = QNetworkRequest(url)
-        self._network_manager.get(name_request)
+        self.checkManualPrinter(address)
 
     def removeManualPrinter(self, key, address = None):
         if key in self._printers:
@@ -94,6 +91,13 @@ class NetworkPrinterOutputDevicePlugin(OutputDevicePlugin):
             self._manual_instances.remove(address)
             self._preferences.setValue("um3networkprinting/manual_instances", ",".join(self._manual_instances))
 
+    def checkManualPrinter(self, address):
+        # Check if a printer exists at this address
+        # If a printer responds, it will replace the preliminary printer created above
+        url = QUrl("http://" + address + self._api_prefix + "system")
+        name_request = QNetworkRequest(url)
+        self._network_manager.get(name_request)
+
     ##  Handler for all requests that have finished.
     def _onNetworkRequestFinished(self, reply):
         reply_url = reply.url().toString()