diff --git a/bstrd/bscache.py b/bstrd/bscache.py
index 7449f39..6675b87 100644
--- a/bstrd/bscache.py
+++ b/bstrd/bscache.py
@@ -71,37 +71,35 @@ class BSCache:
         new_chans = {}
         for name, kwargs in names.items():
             if name not in FIXED_CHANNELS and name not in self.channels:
-                if not is_available(name):
-                    raise ValueError(f"channel {name} is not available")
+                check_availability(name)
                 cfg = make_channel_config(name, *kwargs)
                 new_chans[name] = cfg
 
-        self.update_source_multiple(new_chans)
+        if new_chans:
+            print("add new channels", sorted(new_chans))
+            self.add_vars(new_chans)
+
         return {n: BSVar(n, self) for n in names}
 
 
-    def update_source_multiple(self, chans):
-        self.stop()
-        print("add channels", sorted(chans))
-        self.channels.update(chans)
-        self.start()
-
-
     def get_var(self, name, modulo=None, offset=None):
         if name not in FIXED_CHANNELS and name not in self.channels:
-            if not is_available(name):
-                raise ValueError(f"channel {name} is not available")
+            check_availability(name)
             cfg = make_channel_config(name, modulo, offset)
-            self.update_source(name, cfg)
+            print("add new channel", name)
+            self.add_var(name, cfg)
         return BSVar(name, self)
 
 
-    def update_source(self, name, cfg):
+    def add_vars(self, chans):
         self.stop()
-        print("add channel", name)
-        self.channels[name] = cfg
+        self.channels.update(chans)
         self.start()
 
+    def add_var(self, name, cfg):
+        self.stop()
+        self.channels[name] = cfg
+        self.start()
 
     def rem_vars(self, names):
         self.stop()
@@ -117,12 +115,17 @@ class BSCache:
     def clear_vars(self):
         self.stop()
         self.channels.clear()
+        # cannot start without any channel
 
     def flush(self):
         self.pt.queue.clear()
 
 
 
+def check_availability(name):
+    if not is_available(name):
+        raise ValueError(f"channel {name} is not available")
+
 def is_available(name):
     available = get_available_channels()
     return name in available