Index: firmware/App/Modes/ModeDrain.c
===================================================================
diff -u -r4d7d40a27130dc813d653f044cbb856b1b7d8481 -r4af713cb53b909ba87893dc814d39af89fb8e8d2
--- firmware/App/Modes/ModeDrain.c	(.../ModeDrain.c)	(revision 4d7d40a27130dc813d653f044cbb856b1b7d8481)
+++ firmware/App/Modes/ModeDrain.c	(.../ModeDrain.c)	(revision 4af713cb53b909ba87893dc814d39af89fb8e8d2)
@@ -22,6 +22,7 @@
 #include "OperationModes.h"
 #include "Pressures.h"
 #include "Reservoirs.h"
+#include "TaskGeneral.h"
 #include "TemperatureSensors.h"
 #include "Valves.h"
 
@@ -32,11 +33,15 @@
 
 // ********** private definitions **********
 
-#define TARGET_DRAIN_PUMP_RPM       2800                        ///< Target drain pump speed (in RPM).
+#define TARGET_DRAIN_PUMP_RPM           2800                                                ///< Target drain pump speed (in RPM).
+#define DRAIN_WEIGHT_CHANGE_TOLERANCE   0.1                                                 ///< Weight changes during draining tolerance.
+#define DRAIN_WEIGH_UNCHANGE_TIMEOUT    ( 10 * MS_PER_SECOND / TASK_GENERAL_INTERVAL )      ///< Time period of unchanged weight during draining before timeout.
 
 // ********** private data **********
 
-static DG_DRAIN_STATE_T drainState = DG_DRAIN_STATE_START;      ///< Currently active drain state.
+static DG_DRAIN_STATE_T drainState = DG_DRAIN_STATE_START;                                  ///< Currently active drain state.
+static F32 previousWeight;                                                                  ///< Previous weight of the reservoir draining.
+static U32 weightNotDroppingTimerCounter;                                                   ///< Timer counter for the period weight not dropping.
 
 // ********** private function prototypes **********
 
@@ -52,6 +57,8 @@
 void initDrainMode( void )
 {
     drainState = DG_DRAIN_STATE_START;
+    previousWeight = 0.0;
+    weightNotDroppingTimerCounter = 0;
 }
 
 /*********************************************************************//**
@@ -117,15 +124,31 @@
 {
     DG_DRAIN_STATE_T result = DG_DRAIN_STATE_DRAIN;
     LOAD_CELL_ID_T drainWeightLoadCell = LOAD_CELL_A1;
+    F32 currentFilteredWeight;
+    U32 const targetWeight = getReservoirDrainVolumeTargetMl();
 
     // determine which load cell to use for drain volume - we want weight of inactive reservoir
     if ( RESERVOIR_1 == getActiveReservoir() )
     {
         drainWeightLoadCell = LOAD_CELL_B1;
     }
 
+    currentFilteredWeight = getLoadCellFilteredWeight( drainWeightLoadCell );
+
+    // if weight stays the same for 10 seconds, timeout and auto calibration
+    if ( fabs( previousWeight - currentFilteredWeight ) < DRAIN_WEIGHT_CHANGE_TOLERANCE )
+    {
+        previousWeight = currentFilteredWeight;
+
+        if ( ++weightNotDroppingTimerCounter >= DRAIN_WEIGH_UNCHANGE_TIMEOUT )
+        {
+            weightNotDroppingTimerCounter = 0;
+            setLoadCellAutoCal( drainWeightLoadCell, currentFilteredWeight - targetWeight );
+        }
+    }
+
     // if we've reached our target drain to volume (by weight), we're done draining - go back to re-circ mode
-    if ( getReservoirDrainVolumeTargetMl() >= getLoadCellFilteredWeight( drainWeightLoadCell ) )
+    if ( targetWeight >= currentFilteredWeight )
     {
         setDrainPumpTargetSpeed( 0 );
         requestNewOperationMode( DG_MODE_CIRC );