diff --git a/src/mcvsphere/connection.py b/src/mcvsphere/connection.py
index d94a885..9cb3274 100644
--- a/src/mcvsphere/connection.py
+++ b/src/mcvsphere/connection.py
@@ -61,6 +61,26 @@ class VMwareConnection:
         self._setup_datastore()
         self._setup_network()
 
+    def ensure_connected(self) -> None:
+        """Reconnect if the cached session has expired server-side.
+
+        ESXi expires idle SOAP sessions; the cached ``ServiceInstance`` then
+        raises ``NotAuthenticated`` on the next call. Probing ``currentSession``
+        is one cheap round-trip — None or a raised fault both mean "dead", so
+        we rebuild the connection (and re-resolve datacenter/datastore/etc).
+        """
+        try:
+            if (
+                self.si is not None
+                and self.content is not None
+                and self.content.sessionManager.currentSession is not None
+            ):
+                return  # session is alive
+        except Exception:
+            pass  # any fault here means the session is unusable
+        logger.info("vSphere session expired; reconnecting to %s", self.settings.vcenter_host)
+        self._connect()
+
     def _setup_datacenter(self) -> None:
         """Find and configure the target datacenter."""
         datacenters = [
diff --git a/src/mcvsphere/connection_manager.py b/src/mcvsphere/connection_manager.py
index cc0fcaa..f660e38 100644
--- a/src/mcvsphere/connection_manager.py
+++ b/src/mcvsphere/connection_manager.py
@@ -48,6 +48,9 @@ class ConnectionManager:
             self._connections[target] = VMwareConnection(
                 self._servers[target].to_settings(self._settings)
             )
+        else:
+            # Cached connection may have a server-expired session; revive it.
+            self._connections[target].ensure_connected()
         return self._connections[target]
 
     def describe(self) -> list[dict[str, Any]]: