diff --git a/cylc/flow/cfgspec/globalcfg.py b/cylc/flow/cfgspec/globalcfg.py
index 0d3260c7590..5c95b3ea9e3 100644
--- a/cylc/flow/cfgspec/globalcfg.py
+++ b/cylc/flow/cfgspec/globalcfg.py
@@ -263,6 +263,13 @@
         .. versionchanged:: 8.0.0
 
            {REPLACES}``abort on inactivity``.
+    ''',
+    'restart timeout': '''
+        How long to wait for intervention on restarting a completed workflow.
+        The timer stops if any task is triggered.
+
+        .. versionadded:: 8.1.0
+
     '''
 }
 
@@ -833,6 +840,8 @@ def default_for(
                     vdr_type = VDR.V_INTERVAL
                     if item == "stall timeout":
                         default = DurationFloat(3600)
+                    elif item == "restart timeout":
+                        default = DurationFloat(120)
                     else:
                         default = None
                 Conf(item, vdr_type, default, desc=desc)
diff --git a/cylc/flow/scheduler.py b/cylc/flow/scheduler.py
index e32277f6c7a..d87746449b6 100644
--- a/cylc/flow/scheduler.py
+++ b/cylc/flow/scheduler.py
@@ -30,7 +30,6 @@
 from time import sleep, time
 import traceback
 from typing import (
-    TYPE_CHECKING,
     Callable,
     Iterable,
     NoReturn,
@@ -138,9 +137,6 @@
     get_utc_mode)
 from cylc.flow.xtrigger_mgr import XtriggerManager
 
-if TYPE_CHECKING:
-    from cylc.flow.task_proxy import TaskProxy
-
 
 class SchedulerStop(CylcError):
     """Scheduler normal stop."""
@@ -158,9 +154,10 @@ class Scheduler:
     EVENT_SHUTDOWN = WorkflowEventHandler.EVENT_SHUTDOWN
     EVENT_ABORTED = WorkflowEventHandler.EVENT_ABORTED
     EVENT_WORKFLOW_TIMEOUT = WorkflowEventHandler.EVENT_WORKFLOW_TIMEOUT
+    EVENT_STALL = WorkflowEventHandler.EVENT_STALL
     EVENT_STALL_TIMEOUT = WorkflowEventHandler.EVENT_STALL_TIMEOUT
+    EVENT_RESTART_TIMEOUT = WorkflowEventHandler.EVENT_RESTART_TIMEOUT
     EVENT_INACTIVITY_TIMEOUT = WorkflowEventHandler.EVENT_INACTIVITY_TIMEOUT
-    EVENT_STALL = WorkflowEventHandler.EVENT_STALL
 
     # Intervals in seconds
     INTERVAL_MAIN_LOOP = 1.0
@@ -240,6 +237,7 @@ class Scheduler:
     is_paused = False
     is_updated = False
     is_stalled = False
+    is_restart_timeout_wait = False
     is_reloaded = False
 
     # main loop
@@ -483,7 +481,8 @@ async def configure(self):
         for event, start_now, log_reset_func in [
             (self.EVENT_INACTIVITY_TIMEOUT, True, LOG.debug),
             (self.EVENT_WORKFLOW_TIMEOUT, True, None),
-            (self.EVENT_STALL_TIMEOUT, False, None)
+            (self.EVENT_STALL_TIMEOUT, False, None),
+            (self.EVENT_RESTART_TIMEOUT, False, None)
         ]:
             interval = self._get_events_conf(event)
             if interval is not None:
@@ -492,6 +491,16 @@ async def configure(self):
                     timer.reset()
                 self.timers[event] = timer
 
+        if self.is_restart and not self.pool.get_all_tasks():
+            # This workflow completed before restart; wait for intervention.
+            with suppress(KeyError):
+                self.timers[self.EVENT_RESTART_TIMEOUT].reset()
+                self.is_restart_timeout_wait = True
+                LOG.warning(
+                    "This workflow already completed.\nIt will shut down"
+                    " again unless you trigger tasks before it times out."
+                )
+
         # Main loop plugins
         self.main_loop_plugins = main_loop.load(
             self.cylc_config.get('main loop', {}),
@@ -511,7 +520,7 @@ async def configure(self):
             self.pause_workflow()
 
         self.profiler.log_memory("scheduler.py: begin run while loop")
-        self.is_updated = True
+        # self.is_updated = True  # NOT NEEDED?
         if self.options.profile_mode:
             self.previous_profile_point = 0
             self.count = 0
@@ -1366,7 +1375,7 @@ async def workflow_shutdown(self):
 
         # Is the workflow ready to shut down now?
         if self.pool.can_stop(self.stop_mode):
-            await self.update_data_structure()
+            await self.update_data_structure(self.is_reloaded)
             self.proc_pool.close()
             if self.stop_mode != StopMode.REQUEST_NOW_NOW:
                 # Wait for process pool to complete,
@@ -1587,11 +1596,33 @@ async def main_loop(self) -> None:
 
             # Update state summary, database, and uifeed
             self.workflow_db_mgr.put_task_event_timers(self.task_events_mgr)
-            has_updated = await self.update_data_structure()
-            if has_updated and not self.is_stalled:
-                # Stop the stalled timer.
+
+            updated_task_list = [
+                t for t in self.pool.get_tasks() if t.state.is_updated]
+            has_updated = updated_task_list or self.is_updated
+
+            if updated_task_list and self.is_restart_timeout_wait:
                 with suppress(KeyError):
-                    self.timers[self.EVENT_STALL_TIMEOUT].stop()
+                    self.timers[self.EVENT_RESTART_TIMEOUT].stop()
+                    self.is_restart_timeout_wait = False
+
+            if has_updated:
+                await self.update_data_structure(self.is_reloaded)
+                # TODO what's this about?
+                if not self.is_reloaded:
+                    # (A reload cannot unstall workflow by itself)
+                    self.is_stalled = False
+                self.is_reloaded = False
+
+                # Reset workflow and task updated flags.
+                self.is_updated = False
+                for itask in updated_task_list:
+                    itask.state.is_updated = False
+
+                if not self.is_stalled:
+                    # Stop the stalled timer.
+                    with suppress(KeyError):
+                        self.timers[self.EVENT_STALL_TIMEOUT].stop()
 
             self.process_workflow_db_queue()
 
@@ -1640,17 +1671,12 @@ async def main_loop(self) -> None:
             self.main_loop_intervals.append(time() - tinit)
             # END MAIN LOOP
 
-    async def update_data_structure(self) -> Union[bool, List['TaskProxy']]:
+    async def update_data_structure(self, reloaded: bool = False):
         """Update DB, UIS, Summary data elements"""
-        updated_tasks = [
-            t for t in self.pool.get_tasks() if t.state.is_updated]
-        has_updated = self.is_updated or updated_tasks
-        reloaded = self.is_reloaded
-        # Add tasks that have moved moved from runahead to live pool.
-        if has_updated or self.data_store_mgr.updates_pending:
+        # Add tasks that have moved from runahead to live pool.
+        if self.data_store_mgr.updates_pending:
             # Collect/apply data store updates/deltas
             self.data_store_mgr.update_data_structure(reloaded=reloaded)
-            self.is_reloaded = False
             # Publish updates:
             if self.data_store_mgr.publish_pending:
                 self.data_store_mgr.publish_pending = False
@@ -1659,17 +1685,9 @@ async def update_data_structure(self) -> Union[bool, List['TaskProxy']]:
                 # Non-async sleep - yield to other threads rather
                 # than event loop
                 sleep(0)
-        if has_updated:
-            # Database update
-            self.workflow_db_mgr.put_task_pool(self.pool)
-            # Reset workflow and task updated flags.
-            self.is_updated = False
-            if not reloaded:  # (A reload cannot unstall workflow by itself)
-                self.is_stalled = False
-            for itask in updated_tasks:
-                itask.state.is_updated = False
-            self.update_data_store()
-        return has_updated
+        # Database update
+        self.workflow_db_mgr.put_task_pool(self.pool)
+        self.update_data_store()
 
     def check_workflow_timers(self):
         """Check timers, and abort or run event handlers as configured."""
@@ -1682,6 +1700,10 @@ def check_workflow_timers(self):
                 raise SchedulerError(f'"{abort_conf}" is set')
             if self._get_events_conf(f"{event} handlers") is not None:
                 self.run_event_handlers(event)
+            if event == self.EVENT_RESTART_TIMEOUT:
+                # Unset wait flag to allow normal shutdown.
+                with suppress(KeyError):
+                    self.is_restart_timeout_wait = False
 
     def check_workflow_stalled(self) -> bool:
         """Check if workflow is stalled or not."""
@@ -1850,27 +1872,25 @@ def stop_clock_done(self):
 
     def check_auto_shutdown(self):
         """Check if we should shut down now."""
-        if self.is_paused:
-            # Don't if paused.
-            return False
-
-        if self.check_workflow_stalled():
-            return False
-
-        if any(
-            itask for itask in self.pool.get_tasks()
-            if itask.state(
-                TASK_STATUS_PREPARING,
-                TASK_STATUS_SUBMITTED,
-                TASK_STATUS_RUNNING
-            )
-            or (
-                itask.state(TASK_STATUS_WAITING)
-                and not itask.state.is_runahead
+        if (
+            self.is_paused or
+            self.is_restart_timeout_wait or
+            self.check_workflow_stalled() or
+            # if more tasks to run (if waiting and not
+            # runahead, then held, queued, or xtriggered).
+            any(
+                itask for itask in self.pool.get_tasks()
+                if itask.state(
+                    TASK_STATUS_PREPARING,
+                    TASK_STATUS_SUBMITTED,
+                    TASK_STATUS_RUNNING
+                )
+                or (
+                    itask.state(TASK_STATUS_WAITING)
+                    and not itask.state.is_runahead
+                )
             )
         ):
-            # Don't if there are more tasks to run (if waiting and not
-            # runahead, then held, queued, or xtriggered).
             return False
 
         # Can shut down.
diff --git a/cylc/flow/workflow_events.py b/cylc/flow/workflow_events.py
index adf2abfed8c..b7631e1fd9f 100644
--- a/cylc/flow/workflow_events.py
+++ b/cylc/flow/workflow_events.py
@@ -202,6 +202,7 @@ class WorkflowEventHandler():
     EVENT_INACTIVITY_TIMEOUT = 'inactivity timeout'
     EVENT_STALL = 'stall'
     EVENT_STALL_TIMEOUT = 'stall timeout'
+    EVENT_RESTART_TIMEOUT = 'restart timeout'
 
     WORKFLOW_EVENT_HANDLER = 'workflow-event-handler'
     WORKFLOW_EVENT_MAIL = 'workflow-event-mail'