diff --git a/app/celery/nightly_tasks.py b/app/celery/nightly_tasks.py
index ef6b6f72d..c6ef22c71 100644
--- a/app/celery/nightly_tasks.py
+++ b/app/celery/nightly_tasks.py
@@ -130,25 +130,35 @@ def delete_letter_notifications_older_than_retention():
 @notify_celery.task(name='timeout-sending-notifications')
 @cronitor('timeout-sending-notifications')
 def timeout_notifications():
-    technical_failure_notifications, temporary_failure_notifications = \
-        dao_timeout_notifications(current_app.config.get('SENDING_NOTIFICATIONS_TIMEOUT_PERIOD'))
+    # TEMPORARY: re-run the following code over small batches of notifications
+    # so that we can cope with a high volume that need processing. We've changed
+    # dao_timeout_notifications to return up to 100K notifications, so this task
+    # will operate on up to 500K - normally we only get around 20K.
+    for _ in range(0, 5):
+        technical_failure_notifications, temporary_failure_notifications = \
+            dao_timeout_notifications(current_app.config.get('SENDING_NOTIFICATIONS_TIMEOUT_PERIOD'))
 
-    notifications = technical_failure_notifications + temporary_failure_notifications
-    for notification in notifications:
-        # queue callback task only if the service_callback_api exists
-        service_callback_api = get_service_delivery_status_callback_api_for_service(service_id=notification.service_id)
-        if service_callback_api:
-            encrypted_notification = create_delivery_status_callback_data(notification, service_callback_api)
-            send_delivery_status_to_service.apply_async([str(notification.id), encrypted_notification],
-                                                        queue=QueueNames.CALLBACKS)
+        notifications = technical_failure_notifications + temporary_failure_notifications
+        for notification in notifications:
+            # queue callback task only if the service_callback_api exists
+            service_callback_api = get_service_delivery_status_callback_api_for_service(service_id=notification.service_id)  # noqa: E501
+            if service_callback_api:
+                encrypted_notification = create_delivery_status_callback_data(notification, service_callback_api)
+                send_delivery_status_to_service.apply_async([str(notification.id), encrypted_notification],
+                                                            queue=QueueNames.CALLBACKS)
 
-    current_app.logger.info(
-        "Timeout period reached for {} notifications, status has been updated.".format(len(notifications)))
-    if technical_failure_notifications:
-        message = "{} notifications have been updated to technical-failure because they " \
-                  "have timed out and are still in created.Notification ids: {}".format(
-                      len(technical_failure_notifications), [str(x.id) for x in technical_failure_notifications])
-        raise NotificationTechnicalFailureException(message)
+        current_app.logger.info(
+            "Timeout period reached for {} notifications, status has been updated.".format(len(notifications)))
+        if technical_failure_notifications:
+            message = "{} notifications have been updated to technical-failure because they " \
+                      "have timed out and are still in created.Notification ids: {}".format(
+                          len(technical_failure_notifications), [str(x.id) for x in technical_failure_notifications])
+            raise NotificationTechnicalFailureException(message)
+
+        if len(notifications) == 0:
+            return
+
+    raise RuntimeError("Some notifications may still be in sending.")
 
 
 @notify_celery.task(name="delete-inbound-sms")
diff --git a/app/dao/notifications_dao.py b/app/dao/notifications_dao.py
index 559d1aabd..325cd076a 100644
--- a/app/dao/notifications_dao.py
+++ b/app/dao/notifications_dao.py
@@ -467,15 +467,21 @@ def dao_delete_notifications_by_id(notification_id):
 
 
 def _timeout_notifications(current_statuses, new_status, timeout_start, updated_at):
+    # TEMPORARY: limit the notifications to 100K as otherwise we
+    # see an issues where the task vanishes after it starts executing
+    # - we believe this is a OOM error but there are no logs. From
+    # experimentation we've found we can safely process up to 100K.
     notifications = Notification.query.filter(
         Notification.created_at < timeout_start,
         Notification.status.in_(current_statuses),
-        Notification.notification_type != LETTER_TYPE
-    ).all()
+        Notification.notification_type.in_([SMS_TYPE, EMAIL_TYPE])
+    ).limit(100000).all()
+
     Notification.query.filter(
         Notification.created_at < timeout_start,
         Notification.status.in_(current_statuses),
-        Notification.notification_type != LETTER_TYPE
+        Notification.notification_type.in_([SMS_TYPE, EMAIL_TYPE]),
+        Notification.id.in_([n.id for n in notifications]),
     ).update(
         {'status': new_status, 'updated_at': updated_at},
         synchronize_session=False