diff --git a/reframe/core/logging.py b/reframe/core/logging.py
index ec1273602a..895293c8c9 100644
--- a/reframe/core/logging.py
+++ b/reframe/core/logging.py
@@ -408,10 +408,10 @@ def error(self, msg, *args, **kwargs):
         return self.log(ERROR, msg, *args, **kwargs)
 
     def warning(self, msg, *args, **kwargs):
-        return self.log(WARNING, msg, *args, **kwargs)
+        self.log(WARNING, msg, *args, **kwargs)
 
     def info(self, msg, *args, **kwargs):
-        return self.log(INFO, msg, *args, **kwargs)
+        self.log(INFO, msg, *args, **kwargs)
 
     def verbose(self, message, *args, **kwargs):
         self.log(VERBOSE, message, *args, **kwargs)
@@ -423,6 +423,10 @@ def debug2(self, message, *args, **kwargs):
         self.log(DEBUG2, message, *args, **kwargs)
 
 
+# This is a cache for warnings that we don't want to repeat
+_WARN_ONCE = set()
+
+
 class LoggerAdapter(logging.LoggerAdapter):
     def __init__(self, logger=None, check=None):
         super().__init__(
@@ -550,7 +554,13 @@ def debug2(self, message, *args, **kwargs):
     def verbose(self, message, *args, **kwargs):
         self.log(VERBOSE, message, *args, **kwargs)
 
-    def warning(self, message, *args, **kwargs):
+    def warning(self, message, *args, cache=False, **kwargs):
+        if cache:
+            if message in _WARN_ONCE:
+                return
+
+            _WARN_ONCE.add(message)
+
         message = '%s: %s' % (sys.argv[0], message)
         if self.colorize:
             message = color.colorize(message, color.YELLOW)
@@ -594,6 +604,7 @@ def __init__(self, check=None, level=DEBUG):
         self._orig_logger = _context_logger
         if check is not None:
             _context_logger = LoggerAdapter(_logger, check)
+            _context_logger.colorize = self._orig_logger.colorize
 
     def __enter__(self):
         return _context_logger
diff --git a/reframe/core/modules.py b/reframe/core/modules.py
index 35e019ec8d..e4cc552310 100644
--- a/reframe/core/modules.py
+++ b/reframe/core/modules.py
@@ -1008,6 +1008,14 @@ def unload_all(self):
 class NoModImpl(ModulesSystemImpl):
     '''A convenience class that implements a no-op a modules system.'''
 
+    def _warn(self, msg):
+        getlogger().warning(
+            f"no modules system is set: {msg}: "
+            f"check the 'modules_system' configuration "
+            f"parameter for your system",
+            cache=True
+        )
+
     def available_modules(self, substr):
         return []
 
@@ -1021,10 +1029,10 @@ def _execute(self, cmd, *args):
         return ''
 
     def load_module(self, module):
-        pass
+        self._warn(f'module {module.name!r} will not be loaded')
 
     def unload_module(self, module):
-        pass
+        self._warn(f'module {module.name!r} will not be unloaded')
 
     def is_module_loaded(self, module):
         #
@@ -1043,21 +1051,23 @@ def modulecmd(self, *args):
         return ''
 
     def unload_all(self):
-        pass
+        self._warn('no module will be purged')
 
     def searchpath(self):
         return []
 
     def searchpath_add(self, *dirs):
-        pass
+        self._warn('MODULEPATH will not be modified')
 
     def searchpath_remove(self, *dirs):
-        pass
+        self._warn('MODULEPATH will not be modified')
 
     def emit_load_instr(self, module):
+        self._warn(f'module {module.name!r} will not be loaded')
         return []
 
     def emit_unload_instr(self, module):
+        self._warn(f'module {module.name!r} will not be unloaded')
         return []
 
 
diff --git a/unittests/test_logging.py b/unittests/test_logging.py
index 0b91e2d781..caa374fb05 100644
--- a/unittests/test_logging.py
+++ b/unittests/test_logging.py
@@ -328,6 +328,18 @@ def test_handler_noappend(make_exec_ctx, config_file, logfile):
     assert _found_in_logfile('bar', logfile)
 
 
+def test_warn_once(default_exec_ctx, logfile):
+    rlog.configure_logging(rt.runtime().site_config)
+    rlog.getlogger().warning('foo', cache=True)
+    rlog.getlogger().warning('foo', cache=True)
+    rlog.getlogger().warning('foo', cache=True)
+    _flush_handlers()
+    _close_handlers()
+
+    with open(logfile, 'rt') as fp:
+        assert len(re.findall('foo', fp.read())) == 1
+
+
 def test_date_format(default_exec_ctx, logfile):
     rlog.configure_logging(rt.runtime().site_config)
     rlog.getlogger().warning('foo')