Index: firmware/App/Modes/ModeGenIdle.c
===================================================================
diff -u -r24e8fcb5744724be72ea26bebd95ec594c2c26fe -ra1452dc7f16d37db53930c3d73992098709d7915
--- firmware/App/Modes/ModeGenIdle.c	(.../ModeGenIdle.c)	(revision 24e8fcb5744724be72ea26bebd95ec594c2c26fe)
+++ firmware/App/Modes/ModeGenIdle.c	(.../ModeGenIdle.c)	(revision a1452dc7f16d37db53930c3d73992098709d7915)
@@ -47,10 +47,14 @@
 
 #define TARGET_FLUSH_LINES_RO_FLOW_RATE_L       0.6                     ///< Target flow rate for RO pump.
 
+/// The time of HD lost comm before DG transition back to standby.
+#define HD_LOST_COMM_TIMEOUT_MS                 (5 * SEC_PER_MIN * MS_PER_SECOND )
+
 // ********** private data **********
 
 static DG_GEN_IDLE_MODE_STATE_T genIdleState;                           ///< Currently active generation idle state.
 static F32 flushLinesVolumeL = 0.0;                                     ///< Volume of water pumped by RO pump during flush lines state.
+static U32 hdLostCommStartTime_ms = 0;                                  ///< Lost communication with HD start time in ms.
 
 // ********** private function prototypes **********
 
@@ -68,6 +72,7 @@
 {
     genIdleState = DG_GEN_IDLE_MODE_STATE_START;
     flushLinesVolumeL = 0.0;
+    hdLostCommStartTime_ms = 0;
 }
 
 /*********************************************************************//**
@@ -123,10 +128,17 @@
     checkRORejectionRatio();
 
     // Transition to standby mode when HD is not communicating
-    if ( FALSE == isHDCommunicating() )
+    if ( TRUE == isHDCommunicating() )
     {
-        requestNewOperationMode( DG_MODE_STAN );
+        hdLostCommStartTime_ms = getMSTimerCount();
     }
+    else
+    {
+        if ( TRUE == didTimeout( hdLostCommStartTime_ms, HD_LOST_COMM_TIMEOUT_MS ) )
+        {
+            requestNewOperationMode( DG_MODE_STAN );
+        }
+    }
 
     // Execute current generation idle state
     switch ( genIdleState )