Index: firmware/App/Modes/ModeHeatDisinfectActiveCool.c
===================================================================
diff -u -r5109bb981cab2025fcb9de33e303d046085efa18 -r475fae57bc2a2bdd022b16591877ea6e63503bb6
--- firmware/App/Modes/ModeHeatDisinfectActiveCool.c	(.../ModeHeatDisinfectActiveCool.c)	(revision 5109bb981cab2025fcb9de33e303d046085efa18)
+++ firmware/App/Modes/ModeHeatDisinfectActiveCool.c	(.../ModeHeatDisinfectActiveCool.c)	(revision 475fae57bc2a2bdd022b16591877ea6e63503bb6)
@@ -1110,10 +1110,19 @@
 {
     F32 THdTemperatureC = getTemperatureValue( TEMPSENSORS_HEAT_DISINFECT );
 
-    if ( ( THdTemperatureC <= ROF_ACTIVE_COOL_TARGET_TEMP_C ) && ( FALSE == tempBelowTarget.hasTempTargetTimeBeenSet ) )
+    if ( THdTemperatureC <= ROF_ACTIVE_COOL_TARGET_TEMP_C )
     {
+        // If THd is below the target and the timer for stable temperature has not been set, set it
+        if ( FALSE == tempBelowTarget.hasTempTargetTimeBeenSet )
+        {
+            tempBelowTarget.tempBelowTargetStartTimeMS = getMSTimerCount();
+            tempBelowTarget.hasTempTargetTimeBeenSet   = TRUE;
+        }
+    }
+    else
+    {
+        // The temperature is still above the target so keep reseting the timer
         tempBelowTarget.tempBelowTargetStartTimeMS = getMSTimerCount();
-        tempBelowTarget.hasTempTargetTimeBeenSet   = TRUE;
     }
 
     if ( DG_RESERVOIR_BELOW_TARGET == rsrvrsStatus.rsrvr[ rsrvrID ].rStatus )