diff --git a/coapthon/client/coap.py b/coapthon/client/coap.py
index 7456490..5a3747c 100644
--- a/coapthon/client/coap.py
+++ b/coapthon/client/coap.py
@@ -65,6 +65,13 @@ class CoAP(object):
 
         self._receiver_thread = None
 
+    def purge_transactions(self, timeout_time=defines.EXCHANGE_LIFETIME):
+        """
+        Clean old transactions
+
+        """
+        self._messageLayer.purge(timeout_time)
+
     def close(self):
         """
         Stop the client.
@@ -96,16 +103,21 @@ class CoAP(object):
         assert isinstance(c, int)
         self._currentMID = c
 
-    def send_message(self, message):
+    def send_message(self, message, no_response=False):
         """
         Prepare a message to send on the UDP socket. Eventually set retransmissions.
 
         :param message: the message to send
+        :param no_response: whether to await a response from the request
         """
         if isinstance(message, Request):
             request = self._requestLayer.send_request(message)
             request = self._observeLayer.send_request(request)
             request = self._blockLayer.send_request(request)
+            if no_response:
+                # don't add the send message to the message layer transactions
+                self.send_datagram(request)
+                return
             transaction = self._messageLayer.send_request(request)
             self.send_datagram(transaction.request)
             if transaction.request.type == defines.Types["CON"]:
diff --git a/coapthon/client/helperclient.py b/coapthon/client/helperclient.py
index d204b68..eb79191 100644
--- a/coapthon/client/helperclient.py
+++ b/coapthon/client/helperclient.py
@@ -223,17 +223,26 @@ class HelperClient(object):
         :param request: the request to send
         :param callback: the callback function to invoke upon response
         :param timeout: the timeout of the request
+        :param no_response: whether to await a response from the request
         :return: the response
         """
         if callback is not None:
             thread = threading.Thread(target=self._thread_body, args=(request, callback))
             thread.start()
         else:
-            self.protocol.send_message(request)
+            self.protocol.send_message(request, no_response=no_response)
             if no_response:
                 return
             try:
-                response = self.queue.get(block=True, timeout=timeout)
+                while True:
+                    response = self.queue.get(block=True, timeout=timeout)
+                    if response is not None:
+                        if response.mid == request.mid:
+                            return response
+                        if response.type == defines.Types["NON"]:
+                            return response
+                    else:
+                        return response
             except Empty:
                 #if timeout is set
                 response = None
diff --git a/coapthon/layers/messagelayer.py b/coapthon/layers/messagelayer.py
index c46ea96..966a5f7 100644
--- a/coapthon/layers/messagelayer.py
+++ b/coapthon/layers/messagelayer.py
@@ -42,17 +42,17 @@ class MessageLayer(object):
         self._current_mid %= 65535
         return current_mid
 
-    def purge(self):
+    def purge(self, timeout_time=defines.EXCHANGE_LIFETIME):
         for k in list(self._transactions.keys()):
             now = time.time()
             transaction = self._transactions[k]
-            if transaction.timestamp + defines.EXCHANGE_LIFETIME < now:
+            if transaction.timestamp + timeout_time < now:
                 logger.debug("Delete transaction")
                 del self._transactions[k]
         for k in list(self._transactions_token.keys()):
             now = time.time()
             transaction = self._transactions_token[k]
-            if transaction.timestamp + defines.EXCHANGE_LIFETIME < now:
+            if transaction.timestamp + timeout_time < now:
                 logger.debug("Delete transaction")
                 del self._transactions_token[k]
 
diff --git a/coapthon/serializer.py b/coapthon/serializer.py
index a92726f..3b5e914 100644
--- a/coapthon/serializer.py
+++ b/coapthon/serializer.py
@@ -129,6 +129,9 @@ class Serializer(object):
             return defines.Codes.BAD_REQUEST.number
         except struct.error:
             return defines.Codes.BAD_REQUEST.number
+        except UnicodeDecodeError as e:
+            logger.debug(e)
+            return defines.Codes.BAD_REQUEST.number
 
     @staticmethod
     def serialize(message):