Index: firmware/App/Controllers/AirTrap.c
===================================================================
diff -u -r19a8bf98a7154e24c35da25225d4b55bf70ddd09 -r2d8147c1c9419b59c34d0f4d7dc91d84c57f5391
--- firmware/App/Controllers/AirTrap.c	(.../AirTrap.c)	(revision 19a8bf98a7154e24c35da25225d4b55bf70ddd09)
+++ firmware/App/Controllers/AirTrap.c	(.../AirTrap.c)	(revision 2d8147c1c9419b59c34d0f4d7dc91d84c57f5391)
@@ -36,6 +36,8 @@
 #define AIR_TRAP_DATA_PUB_INTERVAL          ( MS_PER_SECOND / TASK_PRIORITY_INTERVAL )
 /// Persistence period for illegal level sensors fault.
 static const U32 AIR_TRAP_ILLEGAL_LEVELS_PERSISTENCE = ( MS_PER_SECOND * 2 / TASK_PRIORITY_INTERVAL );
+static const U32 AIR_TRAP_UPPER_LEVEL_PERSISTENCE = ( MS_PER_SECOND * 2 / TASK_PRIORITY_INTERVAL );
+
 /// Volume (in mL) of venous portion of blood circuit line.  TODO - get actual volume from Systems.
 #define VENOUS_LINE_VOLUME_ML               ( 200.0F )
 #define DATA_PUBLISH_COUNTER_START_COUNT    7                                                      ///< Data publish counter start count.
@@ -64,6 +66,7 @@
 
 static U32  fillStartTime = 0;                                                              ///< Time stamp for start of air trap fill.
 
+static U32 airTrapUpperLevelCtr = 0;                                                        ///< Timer count for upper level persistence.
 static U32  airTrapIllegalLevelSensorsCtr = 0;                                              ///< Timer counter for illegal level sensor fault.
 
 // ********** private function prototypes **********
@@ -178,6 +181,27 @@
     airTrapLevels[ AIR_TRAP_LEVEL_SENSOR_LOWER ].data = (U32)( TRUE == lower ? AIR_TRAP_LEVEL_AIR : AIR_TRAP_LEVEL_FLUID );
     airTrapLevels[ AIR_TRAP_LEVEL_SENSOR_UPPER ].data = (U32)( TRUE == upper ? AIR_TRAP_LEVEL_AIR : AIR_TRAP_LEVEL_FLUID );
 
+    if ( AIR_TRAP_LEVEL_FLUID == getAirTrapLevel( AIR_TRAP_LEVEL_SENSOR_UPPER ) &&
+         MODE_TREA == getCurrentOperationMode() )
+    {
+        if ( ++airTrapUpperLevelCtr >= AIR_TRAP_UPPER_LEVEL_PERSISTENCE )
+        {
+#ifndef _RELEASE_
+            if ( getSoftwareConfigStatus( SW_CONFIG_DISABLE_ILLEGAL_AIR_TRAP_ALARM ) != SW_CONFIG_ENABLE_VALUE )
+#endif
+            {
+                activateAlarmNoData( ALARM_ID_HD_AIR_TRAP_OVERFILL );
+            }
+        }
+    }
+    else
+    {
+        if ( airTrapUpperLevelCtr > 0 )
+        {
+            airTrapUpperLevelCtr = 0;
+        }
+    }
+
     // Check level readings are valid
     if ( ( AIR_TRAP_LEVEL_AIR == getAirTrapLevel( AIR_TRAP_LEVEL_SENSOR_LOWER ) ) &&
          ( AIR_TRAP_LEVEL_FLUID == getAirTrapLevel( AIR_TRAP_LEVEL_SENSOR_UPPER ) ) )
@@ -347,7 +371,7 @@
         result = AIR_TRAP_MANUAL_CONTROL_STATE;
     }
     // Transition to closed valve state when fluid detected at upper level
-    else if ( AIR_TRAP_LEVEL_FLUID == getAirTrapLevel( AIR_TRAP_LEVEL_SENSOR_UPPER ) )
+    else if ( AIR_TRAP_LEVEL_FLUID == getAirTrapLevel( AIR_TRAP_LEVEL_SENSOR_LOWER ) )
     {
         setValveAirTrap( STATE_CLOSED );
         result = AIR_TRAP_VALVE_CLOSED_STATE;