Index: firmware/App/Modes/ModeStandby.c
===================================================================
diff -u -r46b163d19c65e8c21db7b0247bbb1af0dba1ece5 -ra16225ab0fc1c575ad857ccf1dcccdb7a3aa8eef
--- firmware/App/Modes/ModeStandby.c	(.../ModeStandby.c)	(revision 46b163d19c65e8c21db7b0247bbb1af0dba1ece5)
+++ firmware/App/Modes/ModeStandby.c	(.../ModeStandby.c)	(revision a16225ab0fc1c575ad857ccf1dcccdb7a3aa8eef)
@@ -56,6 +56,8 @@
 static BOOL flushStartReqReceived;                                                             ///< Flag indicates user has requested initiation of flush mode.
 static BOOL heatDisinfectStartReqReceived;                                                     ///< Flag indicates user has requested initiation of heat disinfect mode.
 static BOOL chemDisinfectStartReqReceived;                                                     ///< Flag indicates user has requested initiation of chemical disinfect mode.
+static BOOL disinfectCancelReqPending;                                                         ///< Flag indicates user has requested cancel disinfect mode.
+static U32  disinfectCancelReqID;                                                              ///< ID of requested cancel disinfect mode.
 static DG_DISINFECT_STATE_T dgDisinfectState;                                                  ///< DG disinfect state to be boadcast to UI.
 
 static U32 dataPublishCounter = 0;                                                             ///< Disinfects data publish counter.
@@ -99,6 +101,8 @@
     dataPublishCounter            = 0;
     heatDisinfectStartReqReceived = FALSE;
     chemDisinfectStartReqReceived = FALSE;
+    disinfectCancelReqPending     = FALSE;
+    disinfectCancelReqID          = 0;
     dgDisinfectState              = DG_DISINFECT_NOT_RUNNING_STATE;
 }
 
@@ -159,7 +163,40 @@
 U32 execStandbyMode( void )
 {
     BOOL stop = isStopButtonPressed();
+    CONFIRMATION_REQUEST_STATUS_T confirm_status;
 
+    if ( ( STANDBY_DG_FLUSH_IN_PROGRESS_STATE == currentStandbyState ) ||
+         ( STANDBY_DG_HEAT_DISINFECT_IN_PROGRESS_STATE == currentStandbyState ) ||
+         ( STANDBY_DG_CHEM_DISINFECT_IN_PROGRESS_STATE == currentStandbyState ) )
+    {
+        if ( TRUE == stop )
+        {
+            // Send message to UI to indicate user request to cancel disinfect
+            disinfectCancelReqID = sendConfirmationRequest( CONFIRMATION_REQUEST_TYPE_OPEN, 0 );
+        }
+        else if ( 0 != disinfectCancelReqID )
+        {
+            confirm_status = checkConfirmationRequestStatus( disinfectCancelReqID );
+            switch ( confirm_status )
+            {
+                case CONFIRMATION_REQUEST_STATUS_ACCEPTED :
+                    // TODO cancel disinfect mode
+                    disinfectCancelReqPending = TRUE;
+                    disinfectCancelReqID = 0;
+                    break;
+
+                case CONFIRMATION_REQUEST_STATUS_TIMEOUT :
+                    // send a cancel to UI
+                    break;
+
+                case CONFIRMATION_REQUEST_STATUS_REJECTED :
+                default :
+                    // nothing to do
+                    break;
+            }
+        }
+    }
+
 #ifndef RUN_WITHOUT_DG
     // State machine to get DG to prep a reservoir so we can start a treatment
     switch ( currentStandbyState )
Index: firmware/App/Services/SystemComm.c
===================================================================
diff -u -r46b163d19c65e8c21db7b0247bbb1af0dba1ece5 -ra16225ab0fc1c575ad857ccf1dcccdb7a3aa8eef
--- firmware/App/Services/SystemComm.c	(.../SystemComm.c)	(revision 46b163d19c65e8c21db7b0247bbb1af0dba1ece5)
+++ firmware/App/Services/SystemComm.c	(.../SystemComm.c)	(revision a16225ab0fc1c575ad857ccf1dcccdb7a3aa8eef)
@@ -1141,6 +1141,10 @@
             handleUIServiceModeRequest( message );
             break;
 
+        case MSG_ID_UI_CONFIRMATION_RESULT:
+            handleUIConfirmationResponse( message );
+            break;
+
         // NOTE: this always must be the last case
         case MSG_ID_TESTER_LOGIN_REQUEST:
             handleTesterLogInRequest( message );
Index: firmware/App/Services/SystemCommMessages.c
===================================================================
diff -u -r46b163d19c65e8c21db7b0247bbb1af0dba1ece5 -ra16225ab0fc1c575ad857ccf1dcccdb7a3aa8eef
--- firmware/App/Services/SystemCommMessages.c	(.../SystemCommMessages.c)	(revision 46b163d19c65e8c21db7b0247bbb1af0dba1ece5)
+++ firmware/App/Services/SystemCommMessages.c	(.../SystemCommMessages.c)	(revision a16225ab0fc1c575ad857ccf1dcccdb7a3aa8eef)
@@ -36,6 +36,7 @@
 #include "SystemComm.h"
 #include "SystemCommMessages.h"
 #include "Temperatures.h"
+#include "Timers.h"
 #include "TreatmentEnd.h"
 #include "TreatmentRecirc.h"
 #include "TreatmentStop.h"
@@ -52,6 +53,7 @@
 // ********** private definitions **********
 
 #define MAX_MSGS_BLOCKED_FOR_XMIT       8                   ///< Maximum number of messages to block transmission for.
+#define NUM_CONFIRM_REQUESTS            4                   ///< Number of available confirmation requests.
 
 #pragma pack(push,1)
 /// Payload record structure for block message transmission request.
@@ -67,6 +69,11 @@
 static volatile U16 nextSeqNo = 1;                          ///< Value of sequence number to use for next transmitted message.
 /// List of message IDs that are requested not to be transmitted.
 static BLOCKED_MSGS_DATA_T blockedMessagesForXmit = { 0, 0, 0, 0, 0, 0, 0, 0 };
+static CONFIRMATION_REQUEST_T confirmRequests[NUM_CONFIRM_REQUESTS] =
+                                                   { 0, 0, CONFIRMATION_REQUEST_STATUS_UNUSED,
+                                                     0, 0, CONFIRMATION_REQUEST_STATUS_UNUSED,
+                                                     0, 0, CONFIRMATION_REQUEST_STATUS_UNUSED,
+                                                     0, 0, CONFIRMATION_REQUEST_STATUS_UNUSED, };
 
 // ********** private function prototypes **********
 
@@ -76,6 +83,93 @@
 
 /*********************************************************************//**
  * @brief
+ * The checkConfrimRequestStatus function checks the status of a confirmation request
+ * @details Inputs: confirmRequests[]
+ * @details Outputs: confirmRequests[] cleared if read.
+ * @param request ID
+ * @return CONFIRMATION_REQUEST_STATUS_T
+ *************************************************************************/
+CONFIRMATION_REQUEST_STATUS_T checkConfirmationRequestStatus( U32 request_id )
+{
+    U08 i;
+    CONFIRMATION_REQUEST_STATUS_T status = CONFIRMATION_REQUEST_STATUS_PENDING;
+
+    for ( i=0; i<NUM_CONFIRM_REQUESTS; i++ )
+    {
+        if ( confirmRequests[ i ].requestID == request_id )
+        {
+            if ( TRUE == didTimeout( confirmRequests[ i ].timeStamp, CONFIRMATION_REQUEST_TIMEOUT_MS ) )
+            {
+                status = CONFIRMATION_REQUEST_STATUS_TIMEOUT;
+            }
+            else
+            {
+                status = confirmRequests[ i ].status;
+            }
+            if ( CONFIRMATION_REQUEST_STATUS_PENDING != status)
+            {
+                // Clear the confirmation request
+                confirmRequests[ i ].requestID = 0;
+                confirmRequests[ i ].timeStamp = 0;
+                confirmRequests[ i ].status = CONFIRMATION_REQUEST_STATUS_UNUSED;
+            }
+        }
+    }
+
+    return status;
+}
+
+/*********************************************************************//**
+ * @brief
+ * The sendConfirmationRequest function sends a confirmation request to UI
+ * @details Inputs:
+ * @details Outputs: confirmRequests[].
+ * @param
+ * @return request ID - will be non-zero if sent
+ *************************************************************************/
+U32 sendConfirmationRequest( CONFIRMATION_REQUEST_TYPE_T request_type, U32 reject_reason )
+{
+    MESSAGE_T msg;
+    U08 *payloadPtr = msg.payload;
+    U08 i;
+    static U32 request_id = 0;
+    U32 new_id = 0;
+
+    for ( i=0; i<NUM_CONFIRM_REQUESTS; i++ )
+    {
+        if ( confirmRequests[ i ].status == CONFIRMATION_REQUEST_STATUS_UNUSED )
+        {
+            request_id++;
+            // Save the confirmation request info
+            confirmRequests[ i ].requestID = request_id;
+            confirmRequests[ i ].timeStamp = getMSTimerCount();
+            confirmRequests[ i ].status = CONFIRMATION_REQUEST_STATUS_PENDING;
+            new_id = request_id;
+
+            // Create a message record
+            blankMessage( &msg );
+            msg.hdr.msgID = MSG_ID_HD_REQUEST_UI_CONFIRMATION;
+            // The payload length is U32 Request ID, U32 Type, U32 Reject Reason
+            msg.hdr.payloadLen = 3 * sizeof( U32 );
+
+            memcpy( payloadPtr, &request_id, sizeof( U32 ) );
+            payloadPtr += sizeof( U32 );
+            memcpy( payloadPtr, &request_type, sizeof( U32 ) );
+            payloadPtr += sizeof( U32 );
+            memcpy( payloadPtr, &reject_reason, sizeof( U32 ) );
+
+            // Serialize the message (w/ sync, CRC, and appropriate CAN padding) and add serialized message data to appropriate comm buffer
+            serializeMessage( msg, COMM_BUFFER_OUT_CAN_HD_2_UI, ACK_NOT_REQUIRED );
+
+            break;
+        }
+    }
+
+    return new_id;
+}
+
+/*********************************************************************//**
+ * @brief
  * The serializeMessage function serializes a given message into a given
  * array of bytes.  A sequence # is added to the message here and the ACK
  * bit of the sequence # is set if ACK is required per parameter.  A sync byte
@@ -7324,4 +7418,48 @@
     return result;
 }
 
+/*********************************************************************//**
+ * @brief
+ * The handleUIConfirmationResponse function handles a UI response for
+ * confirmation request.
+ * @details Inputs: none
+ * @details Outputs: message handled
+ * @param message a pointer to the message to handle
+ * @return none
+ *************************************************************************/
+void handleUIConfirmationResponse( MESSAGE_T *message )
+{
+    BOOL result = FALSE;
+
+    if ( message->hdr.payloadLen == 2 * sizeof(U32) )
+    {
+        U32 request_id;
+        CONFIRMATION_REQUEST_STATUS_T status;
+        U08 i;
+
+        memcpy( &request_id, message->payload, sizeof(U32) );
+        memcpy( &status, ( message->payload + sizeof(U32) ), sizeof(U32) );
+
+        for ( i=0; i<NUM_CONFIRM_REQUESTS; i++ )
+        {
+            if ( confirmRequests[ i ].requestID == request_id )
+            {
+                if ( ( CONFIRMATION_REQUEST_STATUS_REJECTED == status ) ||
+                     ( CONFIRMATION_REQUEST_STATUS_ACCEPTED == status ) )
+                {
+                    confirmRequests[ i ].status = status;
+                }
+                else
+                {
+                    // illegal response
+                    // TODO set alarm?
+                }
+            }
+        }
+    }
+
+    // TODO is ACK needed?
+    sendAckResponseMsg( (MSG_ID_T)message->hdr.msgID, COMM_BUFFER_OUT_CAN_HD_2_UI, result );
+}
+
 /**@}*/
Index: firmware/App/Services/SystemCommMessages.h
===================================================================
diff -u -r46b163d19c65e8c21db7b0247bbb1af0dba1ece5 -ra16225ab0fc1c575ad857ccf1dcccdb7a3aa8eef
--- firmware/App/Services/SystemCommMessages.h	(.../SystemCommMessages.h)	(revision 46b163d19c65e8c21db7b0247bbb1af0dba1ece5)
+++ firmware/App/Services/SystemCommMessages.h	(.../SystemCommMessages.h)	(revision a16225ab0fc1c575ad857ccf1dcccdb7a3aa8eef)
@@ -66,6 +66,36 @@
 #define ACK_REQUIRED                    TRUE                ///< Macro for functions that want to know if an outgoing message requires acknowledgement from receiver.
 #define ACK_NOT_REQUIRED                FALSE               ///< Macro for functions that want to know if an outgoing message requires acknowledgement from receiver.
 
+/// TODO - should this be in HDDefs? MsgDefs or other common?.
+#define CONFIRMATION_REQUEST_TIMEOUT_MS    ( SEC_PER_MIN * MS_PER_SECOND )
+/// List of confirmation status.
+typedef enum Confirmation_Status
+{
+    CONFIRMATION_REQUEST_STATUS_REJECTED = 0,          ///< Confirmation status rejected
+    CONFIRMATION_REQUEST_STATUS_ACCEPTED,              ///< Confirmation status accepted
+    CONFIRMATION_REQUEST_STATUS_TIMEOUT,               ///< Confirmation status timeout
+    CONFIRMATION_REQUEST_STATUS_PENDING,               ///< Confirmation status pending response
+    CONFIRMATION_REQUEST_STATUS_UNUSED,                ///< Confirmation status Unused
+    NUM_OF_CONFIRMATION_REQUEST_STATUS                 ///< Number of confirmation status
+} CONFIRMATION_REQUEST_STATUS_T;
+
+/// List of confirmation status.
+typedef enum Confirmation_Request_Type
+{
+    CONFIRMATION_REQUEST_TYPE_OPEN = 0,                ///< Confirmation type open
+    CONFIRMATION_REQUEST_TYPE_CLOSE,                   ///< Confirmation type close
+    CONFIRMATION_REQUEST_TYPE_REJECT,                  ///< Confirmation type cancel
+    NUM_OF_CONFIRMATION_TYPE                           ///< Number of confirmation types
+} CONFIRMATION_REQUEST_TYPE_T;
+
+/// Structure for confirmation request.
+typedef struct
+{
+    U32 requestID;                                      ///< Request ID
+    U32 timeStamp;                                      ///< Timestamp for request
+    CONFIRMATION_REQUEST_STATUS_T status;               ///< Request status (pending, accepted, rejected)
+} CONFIRMATION_REQUEST_T;
+
 // ********** public function prototypes **********
 
 // Serialize message
@@ -813,6 +843,11 @@
 // MSG_ID_HD_SEND_ALARMS_COMMAND
 void handleResendAllAlarmsCommand(  MESSAGE_T* message );
 
+// MSG_ID_UI_CONFIRMATION_RESULT
+void handleUIConfirmationResponse( MESSAGE_T *message );
+CONFIRMATION_REQUEST_STATUS_T checkConfirmationRequestStatus( U32 request_id );
+U32 sendConfirmationRequest( CONFIRMATION_REQUEST_TYPE_T request_type, U32 reject_reason );
+
 /**@}*/
 
 #endif