diff --git a/apps/api/src/services/heartbeat_report_service.py b/apps/api/src/services/heartbeat_report_service.py
index 23229beb2..85167f976 100644
--- a/apps/api/src/services/heartbeat_report_service.py
+++ b/apps/api/src/services/heartbeat_report_service.py
@@ -412,12 +412,12 @@ class HeartbeatReportService:
                     f" ({int(vec_rate*100)}%)"
                 )
 
-        # 2h 沉默（無告警活動）
+        # 24h 沉默（無學習活動）— 2h 太短，正常無事故期間必然誤報
         if report.flywheel.last_learning_at:
             silence_hours = (now_taipei() - report.flywheel.last_learning_at.replace(
                 tzinfo=report.timestamp.tzinfo if report.timestamp.tzinfo else None
             )).total_seconds() / 3600
-            if silence_hours > 2:
+            if silence_hours > 24:
                 warnings.append(f"系統沉默 {silence_hours:.1f}h（無學習活動）")
 
         return warnings