Index: firmware/App/Controllers/BalancingChamber.c
===================================================================
diff -u -r29ac3bdd9dc12a72ad819234914186843625d8e1 -rbdee7caad13de484d50de4089497725c44a43c74
--- firmware/App/Controllers/BalancingChamber.c	(.../BalancingChamber.c)	(revision 29ac3bdd9dc12a72ad819234914186843625d8e1)
+++ firmware/App/Controllers/BalancingChamber.c	(.../BalancingChamber.c)	(revision bdee7caad13de484d50de4089497725c44a43c74)
@@ -207,7 +207,12 @@
     // Fill bicarb chamber once every 60secs.
     if ( bicarbChamberPeriodicFillCounter >= BICARB_CHAMBER_PERIODIC_FILL_TIME )
     {
-        setBicarbChamberFillRequested();
+        if ( FALSE == setBicarbChamberFillRequested() )
+        {
+            // TODO
+            //drybicart state machines are combined and so this is not an issue in future
+            //set alarm ?
+        }
         bicarbChamberPeriodicFillCounter = 0;
     }
 #endif
Index: firmware/App/Controllers/DryBiCart.c
===================================================================
diff -u -r07d08d88c15fdce1e46ec341034c909807694f0a -rbdee7caad13de484d50de4089497725c44a43c74
--- firmware/App/Controllers/DryBiCart.c	(.../DryBiCart.c)	(revision 07d08d88c15fdce1e46ec341034c909807694f0a)
+++ firmware/App/Controllers/DryBiCart.c	(.../DryBiCart.c)	(revision bdee7caad13de484d50de4089497725c44a43c74)
@@ -304,7 +304,6 @@
             if ( TRUE == getU32OverrideValue( &bicarbChamberFillRequested ) )
             {
                 bicarbChamberFillExecState = BICARB_CARTRIDGE_FILL_WATER_START_STATE;
-                bicarbChamberFillRequested.data = FALSE;
             }
             break;
 
@@ -399,11 +398,19 @@
  * flag value to be True.
  * @details \b Inputs: none
  * @details \b Outputs: bicarbChamberFillRequested
- * @return none.
+ * @return TRUE if successful, FALSE if not.
  *************************************************************************/
-void setBicarbChamberFillRequested( void )
+BOOL setBicarbChamberFillRequested( void )
 {
-    bicarbChamberFillRequested.data = TRUE;
+    BOOL result = FALSE;
+
+    if ( FALSE == dryBiCartFillRequested.data && FALSE == dryBiCartDrainRequested.data )
+    {
+        bicarbChamberFillRequested.data = TRUE;
+        result = TRUE;
+    }
+
+    return result;
 }
 
 /*********************************************************************//**
@@ -412,11 +419,19 @@
  * flag value to be True.
  * @details \b Inputs: none
  * @details \b Outputs: dryBiCartFillRequested
- * @return none.
+ * @return TRUE if successful, FALSE if not.
  *************************************************************************/
-void setBicartFillRequested( void )
+BOOL setBicartFillRequested( void )
 {
-    dryBiCartFillRequested.data = TRUE;
+    BOOL result = FALSE;
+
+    if( FALSE == bicarbChamberFillRequested.data && FALSE == dryBiCartDrainRequested.data )
+    {
+        dryBiCartFillRequested.data = TRUE;
+        result = TRUE;
+    }
+
+    return result;
 }
 
 /*********************************************************************//**
@@ -425,11 +440,19 @@
  * flag value to be True.
  * @details \b Inputs: none
  * @details \b Outputs: dryBiCartDrainRequested
- * @return none.
+ * @return TRUE if successful, FALSE if not.
  *************************************************************************/
-void setBicartDrainRequested( void )
+BOOL setBicartDrainRequested( void )
 {
-    dryBiCartDrainRequested.data = TRUE;
+    BOOL result = FALSE;
+
+    if( FALSE == bicarbChamberFillRequested.data && FALSE == dryBiCartFillRequested.data )
+    {
+        dryBiCartDrainRequested.data = TRUE;
+        result = TRUE;
+    }
+
+    return result;
 }
 
 /*********************************************************************//**
@@ -831,6 +854,8 @@
         setValveState( D85_VALV, VALVE_STATE_CLOSED );
         setValveState( D64_VALV, VALVE_STATE_CLOSED);
 
+        bicarbChamberFillRequested.data = FALSE;
+
         state = BICARB_CHAMBER_START_STATE;
     }
 
Index: firmware/App/Controllers/DryBiCart.h
===================================================================
diff -u -r07d08d88c15fdce1e46ec341034c909807694f0a -rbdee7caad13de484d50de4089497725c44a43c74
--- firmware/App/Controllers/DryBiCart.h	(.../DryBiCart.h)	(revision 07d08d88c15fdce1e46ec341034c909807694f0a)
+++ firmware/App/Controllers/DryBiCart.h	(.../DryBiCart.h)	(revision bdee7caad13de484d50de4089497725c44a43c74)
@@ -57,9 +57,9 @@
 U32 execBicarbChamberFillMode( void );
 U32 execDryBicartDrainMode( void );
 void execDryBicart( void );
-void setBicarbChamberFillRequested( void );
-void setBicartFillRequested( void );
-void setBicartDrainRequested( void );
+BOOL setBicarbChamberFillRequested( void );
+BOOL setBicartFillRequested( void );
+BOOL setBicartDrainRequested( void );
 
 DRY_BICART_FILL_EXEC_STATE_T getCurrentDryBiCartFillExecState( void );