diff --git a/src/uas/UASParameterCommsMgr.cc b/src/uas/UASParameterCommsMgr.cc
index 126a6910fc072d2ccb993b866174fd36b19b4aa5..8110651a8b1c9b4fe63f6d9a16425a88548f1b4e 100644
--- a/src/uas/UASParameterCommsMgr.cc
+++ b/src/uas/UASParameterCommsMgr.cc
@@ -11,6 +11,7 @@
 
 UASParameterCommsMgr::UASParameterCommsMgr(QObject *parent) :
     QObject(parent),
+    lastReceiveTime(0),
     mav(NULL),
     maxSilenceTimeout(30000),
     paramDataModel(NULL),
@@ -254,6 +255,7 @@ void UASParameterCommsMgr::silenceTimerExpired()
         int missingReads, missingWrites;
         clearRetransmissionLists(missingReads,missingWrites);
         silenceTimer.stop();
+        lastReceiveTime = 0;
         lastSilenceTimerReset = curTime;
         setParameterStatusMsg(tr("TIMEOUT: Abandoning %1 reads %2 writes after %3 seconds").arg(missingReads).arg(missingWrites).arg(totalElapsed/1000));
     }
@@ -362,14 +364,18 @@ void UASParameterCommsMgr::updateSilenceTimer()
 
 
     if (missReadCount > 0 || missWriteCount > 0) {
-        silenceTimer.start(silenceTimeout);
         lastSilenceTimerReset = QGC::groundTimeMilliseconds();
+        if (0 == lastReceiveTime) {
+            lastReceiveTime = lastSilenceTimerReset;
+        }
+        silenceTimer.start(silenceTimeout);
     }
     else {
         //all parameters have been received, broadcast to UI
         emit parameterListUpToDate();
         resetAfterListReceive();
         silenceTimer.stop();
+        lastReceiveTime = 0;
     }
 
 
diff --git a/src/ui/QGCPX4VehicleConfig.cc b/src/ui/QGCPX4VehicleConfig.cc
index dc0e7b5fed910c63cca71c47e852d3687774e1f1..ceb17af298504b9db7eccdae72234e650ba10a67 100644
--- a/src/ui/QGCPX4VehicleConfig.cc
+++ b/src/ui/QGCPX4VehicleConfig.cc
@@ -426,6 +426,11 @@ void QGCPX4VehicleConfig::startCalibrationRC()
         return;
     }
 
+    // reset all channel mappings above Ch 5 to invalid/unused value before starting calibration
+    for (unsigned int j= 5; j < chanMappedMax; j++) {
+        rcMapping[j] = -1;
+    }
+
     configEnabled = true;
 
     QMessageBox::warning(0,tr("Safety Warning"),