diff --git a/plinth/app.py b/plinth/app.py
index c3d388c44..08ed15ade 100644
--- a/plinth/app.py
+++ b/plinth/app.py
@@ -131,8 +131,8 @@ class App:
 
         Return value must be a list of results. Each result is a two-tuple with
         first value as user visible description of the test followed by the
-        result. The test result is a string enumeration from 'failed', 'passed'
-        and 'error'.
+        result. The test result is a string enumeration from 'failed',
+        'passed', 'error' and 'warning'.
 
         Results are typically collected by diagnosing each component of the app
         and then supplementing the results with any app level diagnostic tests.
diff --git a/plinth/modules/diagnostics/__init__.py b/plinth/modules/diagnostics/__init__.py
index 232c5c6d7..bbf89c2c8 100644
--- a/plinth/modules/diagnostics/__init__.py
+++ b/plinth/modules/diagnostics/__init__.py
@@ -96,11 +96,12 @@ def run_on_all_enabled_modules():
         'progress_percentage': 0
     }
 
-    # Three result strings returned by tests, mark for translation and
+    # Four result strings returned by tests, mark for translation and
     # translate later.
     ugettext_noop('passed')
     ugettext_noop('failed')
     ugettext_noop('error')
+    ugettext_noop('warning')
 
     apps = []
     for app in app_module.App.list():
@@ -127,17 +128,6 @@ def run_on_all_enabled_modules():
             'exception': None,
         }
 
-        try:
-            app_results['diagnosis'] = app.diagnose()
-        except Exception as exception:
-            logger.exception('Error running %s diagnostics - %s', app_id,
-                             exception)
-            app_results['exception'] = str(exception)
-
-        current_results['results'][app_id].update(app_results)
-        current_results['progress_percentage'] = \
-            int((current_index + 1) * 100 / len(apps))
-
     global running_task
     running_task = None
 
diff --git a/plinth/modules/diagnostics/templates/diagnostics_results.html b/plinth/modules/diagnostics/templates/diagnostics_results.html
index 488341014..a46019469 100644
--- a/plinth/modules/diagnostics/templates/diagnostics_results.html
+++ b/plinth/modules/diagnostics/templates/diagnostics_results.html
@@ -21,7 +21,7 @@
               <span class="badge badge-success">{% trans result %}</span>
             {% elif result == 'failed' %}
               <span class="badge badge-danger">{% trans result %}</span>
-            {% elif result == 'error' %}
+            {% elif result == 'error' or result == 'warning' %}
               <span class="badge badge-warning">{% trans result %}</span>
             {% else %}
               {{ result }}
diff --git a/plinth/modules/letsencrypt/__init__.py b/plinth/modules/letsencrypt/__init__.py
index fc66f3fe8..52f259531 100644
--- a/plinth/modules/letsencrypt/__init__.py
+++ b/plinth/modules/letsencrypt/__init__.py
@@ -91,6 +91,10 @@ class LetsEncryptApp(app_module.App):
             if domain.domain_type.can_have_certificate:
                 results.append(diagnose_url('https://' + domain.name))
 
+        if not results:
+            results.append(
+                (_('Cannot test: No domains are configured.'), 'warning'))
+
         return results