Index: firmware/App/Modes/Dialysis.c
===================================================================
diff -u -r1a36e9bd718b40ceaee21dd12eca2da353828e30 -rf3d625e2593ced120c4a98b9ed7e28b132445642
--- firmware/App/Modes/Dialysis.c	(.../Dialysis.c)	(revision 1a36e9bd718b40ceaee21dd12eca2da353828e30)
+++ firmware/App/Modes/Dialysis.c	(.../Dialysis.c)	(revision f3d625e2593ced120c4a98b9ed7e28b132445642)
@@ -103,6 +103,7 @@
 static F32 setUFRate;                                   ///< Currently set ultrafiltration rate (from prescription).
 
 static BOOL autoResumeUF;                               ///< Flag indicates UF should be auto-resumed after saline bolus completes.
+static BOOL airTrapFillInProgress;                      ///< Flag indicates an air trap fill is in progress.
 static BLOOD_LEAK_ZEROING_T bloodLeakZeroingStatus;     ///< Blood leak zeroing status.
 
 // ********** private function prototypes **********
@@ -160,6 +161,7 @@
     resetDialOutRateOffset();
 
     autoResumeUF = FALSE;
+    airTrapFillInProgress = FALSE;
 
     for ( i = 0; i < NUM_OF_LOAD_CELLS; i++ )
     {
@@ -217,6 +219,8 @@
     lastUFTimeStamp = getMSTimerCount();
     // Send dialysate outlet pump latest UF volumes
     setDialOutUFVolumes( refUFVolume, measUFVolume );
+    // initialize air trap fill flag
+    airTrapFillInProgress = FALSE;
 
     resetReservoirsVariables();
 
@@ -572,6 +576,7 @@
         bloodLeakZeroingStatus.zeroingRequestState = BLOOD_LEAK_ZEROING_RQST_REQUESTED;
     }
 
+    // Check for blood leak zeroing request
     if ( ( BLOOD_LEAK_ZEROING_RQST_REQUESTED == bloodLeakZeroingStatus.zeroingRequestState ) && ( DIALYSIS_UF_STATE == currentDialysisState ) )
     {
         if ( TRUE == checkHasReservoirBeenSwitched() )
@@ -607,6 +612,8 @@
     // Calculate UF measured volume and provide to dialysate outlet pump controller (watch UF regardless of dialysis state)
     updateUFVolumes();
 
+    airTrapFillInProgress = isAirTrapFillInProgress();
+
     if ( priorSubState != currentDialysisState )
     {
         setCurrentSubState( (U32)currentDialysisState );
@@ -639,6 +646,23 @@
         setHeparinCompleted();
     }
 
+    // if an air trap fill has started, set BP rate and VBV state accordingly
+    if ( ( airTrapFillInProgress != TRUE ) && ( TRUE == isAirTrapFillInProgress() ) )
+    {
+        // set BP to air trap fill rate if air trap fill has been initiated
+        setBloodPumpTargetFlowRate( AIR_TRAP_FILL_BLOOD_FLOW_RATE, MOTOR_DIR_FORWARD, PUMP_CONTROL_MODE_CLOSED_LOOP );
+        // close VBV for fill
+        setValvePosition( VBV, VALVE_POSITION_C_CLOSE );
+    }
+    // if an air trap fill has completed, restore BP and VBV to blood prime ramp settings
+    if ( ( TRUE == airTrapFillInProgress ) && ( isAirTrapFillInProgress() != TRUE ) )
+    {
+        // restore BP to set blood flow rate
+        setBloodPumpTargetFlowRate( setBloodFlowRate, MOTOR_DIR_FORWARD, PUMP_CONTROL_MODE_CLOSED_LOOP );
+        // re-open VBV for blood recirculation
+        setValvePosition( VBV, VALVE_POSITION_B_OPEN );
+    }
+
     // Handle current ultrafiltration state
     switch ( currentUFState )
     {
@@ -724,7 +748,7 @@
  * @brief
  * The handleUFPausedState function handles the Paused state of the
  * ultrafiltration state machine.
- * @details Inputs: salineBolusStartRequested
+ * @details Inputs: none
  * @details Outputs: if ultrafiltration resumption requested, UF time is set to resume.
  * @param dialysisState next dialysis state
  * @return next ultrafiltration state.