Index: firmware/App/Modes/ModeDrain.c
===================================================================
diff -u -r5c430c3ac17fc8ad836fd70b8a3b8a12af44319e -reeaab2a9a685fb18845888d91040d3aa01977f6d
--- firmware/App/Modes/ModeDrain.c	(.../ModeDrain.c)	(revision 5c430c3ac17fc8ad836fd70b8a3b8a12af44319e)
+++ firmware/App/Modes/ModeDrain.c	(.../ModeDrain.c)	(revision eeaab2a9a685fb18845888d91040d3aa01977f6d)
@@ -7,8 +7,8 @@
 *
 * @file    ModeDrain.c
 *
-* @author  (last)      Dara Navaei
-* @date    (last)      21-Dec-2022
+* @author  (last)      Michael Garthwaite
+* @date    (last)      16-May-2023
 *
 * @author  (original)  Leonardo Baloa
 * @date    (original)  20-Dec-2019
@@ -39,8 +39,8 @@
 
 // ********** private definitions **********
 
-#define TARGET_DRAIN_PUMP_RPM                    2400                                                  ///< Target drain pump speed (in RPM).
-#define DRAIN_WEIGHT_UNCHANGE_TIMEOUT            ( 2 * MS_PER_SECOND )                                 ///< Time period of unchanged weight during draining before timeout.
+#define TARGET_DRAIN_PUMP_RPM                    2200                                                  ///< Target drain pump speed (in RPM).
+#define DRAIN_WEIGHT_UNCHANGE_TIMEOUT_MS         ( 2 * MS_PER_SECOND )                                 ///< Time period of unchanged weight during draining before timeout.
 
 #define DRAIN_EMPTY_TARE_WAIT                    ( MS_PER_SECOND / TASK_GENERAL_INTERVAL )             /// Time period to wait after drain complete and before taring load cells.
 
@@ -55,8 +55,21 @@
 #define RINSE_CONCENTRATE_LINES_WAIT             ( 25 * MS_PER_SECOND / TASK_GENERAL_INTERVAL )        ///< Time period to wait for concentrate lines to rinse.
 
 #define RINSE_SPEED                              ( ( CONCENTRATE_PUMP_MAX_SPEED - 3.0F ) * -1.0F )     ///< Reserver the concentrate speed to rinse out concentrate lines.
-#define CONCENTRATION_BOTTLE_LOW_VOLUME_ML       100.0F                                                ///< Concentration bottle low volume in mL.
 
+#define CONCENTRATE_BOTTLE_PRIMING_VOL_ML        73.0F                                                 ///< Concentrate bottle priming volume in mL.
+#define CONCENTRATE_BOTTLE_RESERVOIOR_VOL_ML     1500.0F                                               ///< Concentrate bottle reservoir volume in mL
+#define CONCENTRATE_BOTTLE_RESERVOIOR_FILLS      3                                                     ///< Concentrate bottle reservoir vlls.
+#define BICARB_PERCENT_FILL                      0.03514F                                              ///< Bicarb volume percentage of reservoir volume.
+#define ACID_PERCENT_FILL                        0.02222F                                              ///< Acid volume percentage of reservoir volume.
+
+///< Concentrate bottle acid low volume in mL.
+static const F32 CONCENTRATE_BOTTLE_ACID_LOW_VOLUME_ML   = ( CONCENTRATE_BOTTLE_PRIMING_VOL_ML +
+                                                             ( CONCENTRATE_BOTTLE_RESERVOIOR_VOL_ML * CONCENTRATE_BOTTLE_RESERVOIOR_FILLS * ACID_PERCENT_FILL) );
+
+///< Concentrate bottle bicarb low volume in mL.
+static const F32 CONCENTRATE_BOTTLE_BICARB_LOW_VOLUME_ML = ( CONCENTRATE_BOTTLE_PRIMING_VOL_ML +
+                                                             ( CONCENTRATE_BOTTLE_RESERVOIOR_VOL_ML * CONCENTRATE_BOTTLE_RESERVOIOR_FILLS * BICARB_PERCENT_FILL) );
+
 // ********** private data **********
 
 static DG_DRAIN_STATE_T drainState;                                                                    ///< Currently active drain state.
@@ -100,6 +113,7 @@
 {
     // re-initialize each time we transition to drain mode
     initDrainMode();
+    setCurrentSubState( NO_SUB_STATE );
 
     DG_RESERVOIR_ID_T inactiveReservoir = getInactiveReservoir();
 
@@ -122,9 +136,13 @@
     // because the initial guess in the heaters driver needs the target flow to calculate
     // the new PWMs for the main and small primary heaters
     setROPumpTargetFlowRateLPM( TARGET_RO_FLOW_RATE_L, TARGET_RO_PRESSURE_PSI );
-    setHeaterTargetTemperature( DG_PRIMARY_HEATER, getPrimaryHeaterTargetTemperature() );
-    startHeater( DG_PRIMARY_HEATER );
 
+    if ( FALSE == isHeaterOn( DG_PRIMARY_HEATER ) )
+    {
+        setHeaterTargetTemperature( DG_PRIMARY_HEATER, getPrimaryHeaterTargetTemperature() );
+        startHeater( DG_PRIMARY_HEATER );
+    }
+
     setCPLDCleanLEDColor( CPLD_CLEAN_LED_OFF );
 
     return drainState;
@@ -232,7 +250,7 @@
     DG_RESERVOIR_ID_T inactiveReservoir = getInactiveReservoir();
 
     // if we have reached our target drain to volume (by weight) or cannot drain anymore, we are done draining - go back to generation idle mode
-    if ( TRUE == hasTargetDrainVolumeBeenReached( inactiveReservoir, DRAIN_WEIGHT_UNCHANGE_TIMEOUT ) )
+    if ( TRUE == hasTargetDrainVolumeBeenReached( inactiveReservoir, DRAIN_WEIGHT_UNCHANGE_TIMEOUT_MS ) )
     {
         DG_ACID_CONCENTRATES_RECORD_T acid;
         F32 acidBottleVolML;
@@ -246,7 +264,6 @@
         acidBottleVolML   = acid.acidConcentrate[ CAL_DATA_ACID_CONCENTRATE_1 ].acidFullBottleVolumeML;
         bicarbBottleVolML = bicarb.bicarbConcentrate[ CAL_DATA_BICARB_CONCENTRATE_1 ].bicarbStartVolumeML;
 
-
         if ( DG_RESERVOIR_1 == inactiveReservoir )
         {
             setValveState( VRD1, VALVE_STATE_CLOSED );
@@ -261,14 +278,14 @@
 #endif
         {
             // Detect empty bottles using integrated volumes
-            if ( ( acidBottleVolML - getChemicalUsedVolumeML( ACID ) ) <= CONCENTRATION_BOTTLE_LOW_VOLUME_ML ) // ||  // SRSDG 437
+            if ( ( acidBottleVolML - getChemicalUsedVolumeML( ACID ) ) <= CONCENTRATE_BOTTLE_ACID_LOW_VOLUME_ML ) // SRSDG 836
             {
                 resetChemicalUsedVolumeML( ACID );
                 setThisFisrtFillFlag( TRUE );                                 // indicates bottles need prime
                 activateAlarmNoData( ALARM_ID_DG_ACID_BOTTLE_LOW_VOLUME );
             }
 
-            if ( ( bicarbBottleVolML - getChemicalUsedVolumeML( BICARB ) ) <= CONCENTRATION_BOTTLE_LOW_VOLUME_ML )  // || // SRSDG 438
+            if ( ( bicarbBottleVolML - getChemicalUsedVolumeML( BICARB ) ) <= CONCENTRATE_BOTTLE_BICARB_LOW_VOLUME_ML )  // SRSDG 837
             {
                 resetChemicalUsedVolumeML( BICARB );
                 setThisFisrtFillFlag( TRUE );