Index: firmware/App/Controllers/AirTrap.c
===================================================================
diff -u -rd710343a990811b05a23c81b4eaef3dd547c474a -r26b903a6c34dce58edfaf6b3038688b43a5b00af
--- firmware/App/Controllers/AirTrap.c	(.../AirTrap.c)	(revision d710343a990811b05a23c81b4eaef3dd547c474a)
+++ firmware/App/Controllers/AirTrap.c	(.../AirTrap.c)	(revision 26b903a6c34dce58edfaf6b3038688b43a5b00af)
@@ -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.
@@ -178,6 +180,20 @@
     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 ( ++airTrapIllegalLevelSensorsCtr >= AIR_TRAP_ILLEGAL_LEVELS_PERSISTENCE )
+        {
+#ifndef _RELEASE_
+            if ( getSoftwareConfigStatus( SW_CONFIG_DISABLE_ILLEGAL_AIR_TRAP_ALARM ) != SW_CONFIG_ENABLE_VALUE )
+#endif
+            {
+                activateAlarmNoData( ALARM_ID_AIR_TRAP_FILL_DURING_TREATMENT );
+            }
+        }
+    }
+
     // 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 ) ) )