Index: firmware/App/Modes/BloodPrime.c
===================================================================
diff -u -re45524455c005d4fa1734efcbaf7ed0499302670 -r764d85698b625d8b8fc1f53d60b6c0f10dad82b8
--- firmware/App/Modes/BloodPrime.c	(.../BloodPrime.c)	(revision e45524455c005d4fa1734efcbaf7ed0499302670)
+++ firmware/App/Modes/BloodPrime.c	(.../BloodPrime.c)	(revision 764d85698b625d8b8fc1f53d60b6c0f10dad82b8)
@@ -37,7 +37,8 @@
 // ********** private definitiions ***********
 
 #define TARGET_BLOOD_PRIME_VOLUME_ML               300.0                    ///< Target blood prime volume to prime the blood side circuit (in mL).
-#define MIN_RAMP_TIME_SEC                          60                       ///< Minimum ramp time for blood prime (in seconds).
+#define MAX_BLOOD_PRIME_VOLUME_ERROR_ML             60.0                    ///< Maximum error in total additional blood prime volume (20% of total).
+#define MIN_RAMP_TIME_SEC                           60                      ///< Minimum ramp time for blood prime (in seconds).
 
 /// Initial flow rate for blood pump when starting blood prime operation.
 #define BLOOD_PRIME_INIT_BP_FLOW_RATE_ML_MIN       100
@@ -63,7 +64,8 @@
 /// Interval (in task intervals) at which to publish blood prime data to CAN bus.
 static OVERRIDE_U32_T bloodPrimePublishInterval = { BLOOD_PRIME_DATA_PUBLISH_INTERVAL, BLOOD_PRIME_DATA_PUBLISH_INTERVAL, BLOOD_PRIME_DATA_PUBLISH_INTERVAL, 0 };
 
-static OVERRIDE_F32_T  cumulativeBloodPrimeVolume_mL = { 0.0, 0.0, 0.0, 0 };    ///< Total cumulative blood prime volume (in mL).
+static OVERRIDE_F32_T  cumulativeBloodPrimeVolume_mL = { 0.0, 0.0, 0.0, 0 };    ///< Total cumulative blood prime volume (in mL) from measured blood flow rate.
+static F32 expectedBloodPrimeVolume_mL = 0.0;                                   ///< Total cumulative blood prime volume (in mL) expected based on target blood flow rate.
 
 // ********** private function prototypes **********
 
@@ -88,6 +90,7 @@
     bloodPrimeRampControlTimerCtr = 0;
     bloodPrimePublishTimerCtr = BLOOD_PRIME_DATA_PUBLISH_INTERVAL;
     cumulativeBloodPrimeVolume_mL.data = 0.0;
+    expectedBloodPrimeVolume_mL = 0.0;
     resetBloodPrimeFlags();
 
     bloodPrimeRampFlowRate_mL_min = (F32)BLOOD_PRIME_INIT_BP_FLOW_RATE_ML_MIN;
@@ -218,6 +221,7 @@
 
     // Update blood prime volume delivered so far
     cumulativeBloodPrimeVolume_mL.data += ( getMeasuredBloodFlowRate() * BLOOD_PRIME_FLOW_INTEGRATOR );
+    expectedBloodPrimeVolume_mL += ( (F32)getTargetBloodFlowRate() * BLOOD_PRIME_FLOW_INTEGRATOR );
 
     // Has blood prime completed?
     if ( getBloodPrimeVolume() >= TARGET_BLOOD_PRIME_VOLUME_ML )
@@ -229,7 +233,7 @@
     }
 #ifndef DISABLE_PUMP_FLOW_CHECKS
     // Is blood prime taking too long based on set BP rate?
-    else if ( TBD )
+    else if ( fabs( expectedBloodPrimeVolume_mL - getBloodPrimeVolume() ) > MAX_BLOOD_PRIME_VOLUME_ERROR_ML )
     {
         activateAlarmNoData( ALARM_ID_BLOOD_PRIME_VOLUME_CHECK_FAILURE );
     }