diff --git a/src/algorithms/telemetry_decoder/gnuradio_blocks/gps_l1_ca_telemetry_decoder_gs.cc b/src/algorithms/telemetry_decoder/gnuradio_blocks/gps_l1_ca_telemetry_decoder_gs.cc
index ee99fac6a..0f082c6df 100644
--- a/src/algorithms/telemetry_decoder/gnuradio_blocks/gps_l1_ca_telemetry_decoder_gs.cc
+++ b/src/algorithms/telemetry_decoder/gnuradio_blocks/gps_l1_ca_telemetry_decoder_gs.cc
@@ -218,8 +218,6 @@ bool gps_l1_ca_telemetry_decoder_gs::decode_subframe()
     uint32_t GPS_frame_4bytes = 0;
     float symbol_accumulator = 0;
     bool subframe_synchro_confirmation = false;
-    bool CRC_ok = true;
-
     for (float subframe_symbol : d_symbol_history)
         {
             // ******* SYMBOL TO BIT *******
@@ -269,11 +267,6 @@ bool gps_l1_ca_telemetry_decoder_gs::decode_subframe()
                                 {
                                     subframe_synchro_confirmation = true;
                                 }
-                            else
-                                {
-                                    // std::cout << "word invalid sat " << this->d_satellite << std::endl;
-                                    CRC_ok = false;
-                                }
                             // add word to subframe
                             // insert the word in the correct position of the subframe
                             std::memcpy(&subframe[word_index * GPS_WORD_LENGTH], &GPS_frame_4bytes, sizeof(uint32_t));
@@ -290,7 +283,7 @@ bool gps_l1_ca_telemetry_decoder_gs::decode_subframe()
 
     // decode subframe
     // NEW GPS SUBFRAME HAS ARRIVED!
-    if (CRC_ok)
+    if (subframe_synchro_confirmation)
         {
             int32_t subframe_ID = d_nav.subframe_decoder(subframe);  //decode the subframe
             if (subframe_ID > 0 and subframe_ID < 6)
@@ -329,21 +322,24 @@ bool gps_l1_ca_telemetry_decoder_gs::decode_subframe()
                         default:
                             break;
                         }
+                    return true;
                 }
             else
                 {
                     return false;
                 }
         }
-
-    return subframe_synchro_confirmation;
 }
 
 
 void gps_l1_ca_telemetry_decoder_gs::reset()
 {
+    gr::thread::scoped_lock lock(d_setlock);  // require mutex with work function called by the scheduler
     d_last_valid_preamble = d_sample_counter;
     d_sent_tlm_failed_msg = false;
+    flag_TOW_set = false;
+    d_symbol_history.clear();
+    d_stat = 0;
     DLOG(INFO) << "Telemetry decoder reset for satellite " << d_satellite;
 }
 
@@ -400,6 +396,7 @@ int gps_l1_ca_telemetry_decoder_gs::general_work(int noutput_items __attribute__
                         DLOG(INFO) << "Preamble detection for GPS L1 satellite " << this->d_satellite;
                         d_stat = 1;  // enter into frame pre-detection status
                     }
+                flag_TOW_set = false;
                 break;
             }
         case 1:  // possible preamble lock
@@ -438,6 +435,7 @@ int gps_l1_ca_telemetry_decoder_gs::general_work(int noutput_items __attribute__
                                 if (preamble_diff > d_preamble_period_symbols)
                                     {
                                         d_stat = 0;  // start again
+                                        flag_TOW_set = false;
                                     }
                             }
                     }
@@ -486,9 +484,16 @@ int gps_l1_ca_telemetry_decoder_gs::general_work(int noutput_items __attribute__
     // 2. Add the telemetry decoder information
     if (d_flag_preamble == true)
         {
-            d_TOW_at_current_symbol_ms = static_cast<uint32_t>(d_nav.d_TOW * 1000.0);
-            d_TOW_at_Preamble_ms = static_cast<uint32_t>(d_nav.d_TOW * 1000.0);
-            flag_TOW_set = true;
+            if (!d_nav.d_TOW == 0)
+                {
+                    d_TOW_at_current_symbol_ms = static_cast<uint32_t>(d_nav.d_TOW * 1000.0);
+                    d_TOW_at_Preamble_ms = static_cast<uint32_t>(d_nav.d_TOW * 1000.0);
+                    flag_TOW_set = true;
+                }
+            else
+                {
+                    DLOG(INFO) << "Received GPS L1 TOW equal to zero at sat " << d_nav.i_satellite_PRN;
+                }
         }
     else
         {