Index: firmware/App/Controllers/Heaters.c
===================================================================
diff -u -r5c53288436774f0cf6a24132ace29a64a66d619d -rf43eb0d0f168ea14b846d0c24f0ad0cb30784d3f
--- firmware/App/Controllers/Heaters.c	(.../Heaters.c)	(revision 5c53288436774f0cf6a24132ace29a64a66d619d)
+++ firmware/App/Controllers/Heaters.c	(.../Heaters.c)	(revision f43eb0d0f168ea14b846d0c24f0ad0cb30784d3f)
@@ -642,7 +642,7 @@
     if ( getSoftwareConfigStatus( SW_CONFIG_DISABLE_HEATERS_EFFICIENCY ) != SW_CONFIG_ENABLE_VALUE )
 #endif
     {
-        if ( TRUE == checkEfficiency )
+        if ( ( TRUE == checkEfficiency ) && ( FALSE == isThisTheFirstFill() ) )
         {
             F32 heaterDutyCycle          = heatersStatus[ DG_PRIMARY_HEATER ].dutycycle;
             F32 lastFillTemperature      = getLastFillTemperature();
@@ -693,8 +693,8 @@
 static F32 calculateTrimmerHeaterDutyCycle( F32 targetTemperature, F32 currentTemperature, F32 flow, BOOL checkEfficiency )
 {
     // Get the primary heater's efficiency and the last fill temperature from the ModeFill
-    F32 heaterEfficiency = heatersStatus[ DG_TRIMMER_HEATER ].heaterEstGain;
-    F32 dutyCycle        = 0.0;
+    F32 heaterEstGain = heatersStatus[ DG_TRIMMER_HEATER ].heaterEstGain;
+    F32 dutyCycle     = 0.0;
 
 #ifndef _RELEASE_
     if ( getSoftwareConfigStatus( SW_CONFIG_DISABLE_HEATERS_EFFICIENCY ) != SW_CONFIG_ENABLE_VALUE )
@@ -708,7 +708,7 @@
 
     // Duty cycle = ( 69.73 * flow rate * deltaT / primary heater maximum power ) and multiply the duty cycle to the heater efficiency
     dutyCycle = ( ( flow * WATER_SPECIFIC_HEAT_DIVIDED_BY_MINUTES *
-                  ( targetTemperature - currentTemperature ) * heaterEfficiency ) / TRIMMER_HEATER_MAX_POWER_W ) * heaterEfficiency;
+                  ( targetTemperature - currentTemperature ) ) / TRIMMER_HEATER_MAX_POWER_W ) * heaterEstGain;
 
     // Check the boundaries of the calculated duty cycle
     dutyCycle = MIN( dutyCycle, HEATERS_MAX_DUTY_CYCLE );