Index: firmware/App/Controllers/Heaters.c
===================================================================
diff -u -r4eab0a5086a5fddeea6cbdf3f79ce1067851b4be -rc28fa96d9ed38b8bfa793eb9096e32967e2e40cb
--- firmware/App/Controllers/Heaters.c	(.../Heaters.c)	(revision 4eab0a5086a5fddeea6cbdf3f79ce1067851b4be)
+++ firmware/App/Controllers/Heaters.c	(.../Heaters.c)	(revision c28fa96d9ed38b8bfa793eb9096e32967e2e40cb)
@@ -8,7 +8,7 @@
 * @file    Heaters.c
 *
 * @author  (last)      Dara Navaei
-* @date    (last)      03-Feb-2023
+* @date    (last)      09-Feb-2023
 *
 * @author  (original)  Dara Navaei
 * @date    (original)  23-Apr-2020
@@ -55,6 +55,7 @@
 #define HEATERS_MIN_EST_GAIN                                       0.2F                                                            ///< Heaters minimum estimation gain.
 #define HEATERS_MAX_EST_GAIN                                       5.0F                                                            ///< Heaters maximum estimation gain.
 #define HEATERS_NEUTRAL_EST_GAIN                                   1.0F                                                            ///< Heaters neutral estimation gain.
+#define HEATERS_ZERO_DELTA_TEMP_C                                  0.0F                                                            ///< Heaters zero delta temperature in C.
 
 #define HEATERS_DATA_PUBLISH_INTERVAL                              ( MS_PER_SECOND / TASK_PRIORITY_INTERVAL )                      ///< Heaters data publish interval.
 
@@ -68,6 +69,7 @@
 #define TRIMMER_HEATER_MAX_POWER_W                                 66.5F                                                           ///< Trimmer heater maximum power in Watts.
 #define TRIMMER_HEATER_INITIAL_CONTROL_INTERVAL_COUNT              ( ( 10 * MS_PER_SECOND ) / TASK_GENERAL_INTERVAL )              ///< Trimmer heater initial control interval count.
 #define TRIMMER_HEATER_CONTROL_INTERVAL_COUNT                      ( ( 30 * MS_PER_SECOND ) / TASK_GENERAL_INTERVAL )              ///< Trimmer heater control interval count.
+#define TRIMMER_HEATER_MIN_DIALYSATE_FLOWRATE_LPM                  0.05F                                                           ///< Trimmer heater minimum dialysate flow rate in L/min.
 
 #define DELTA_TEMPERATURE_TIME_COSNTANT_C                          8.6F                                                            ///< Delta temperature calculated from time constant.
 #define PRIMARY_HEATER_DUTY_CYCLE_PER_TEMPERATURE_C                0.015F                                                          ///< Primary heaters duty cycle per temperature in C.
@@ -373,7 +375,7 @@
             {
                 alarm     = ALARM_ID_DIALYSATE_FLOW_TOO_LOW_WHILE_TRIMMER_HEATER_IS_ON;
                 measFlow  = getMeasuredRawFlowRateLPM( DIALYSATE_FLOW_SENSOR );
-                minFlow   = MIN_DIALYSATE_FLOWRATE_LPM;
+                minFlow   = TRIMMER_HEATER_MIN_DIALYSATE_FLOWRATE_LPM;
                 isFlowLow = ( measFlow > minFlow ? FALSE : TRUE );
             }
 
@@ -782,10 +784,12 @@
 {
     // Duty cycle = ( 69.73 * flow rate * deltaT / primary heater maximum power ) ^ 1/2
     // Multiply the duty cycle to the heater efficiency
-    F32 dutyCycle = sqrt( ( WATER_SPECIFIC_HEAT_DIVIDED_BY_MINUTES * fabs( targetTemperature - currentTemperature ) * flow ) / PRIMARY_HEATERS_MAXIMUM_POWER_WATTS );
-    dutyCycle    *= heatersStatus[ DG_PRIMARY_HEATER ].heaterEstGain;
-    dutyCycle     = MIN( dutyCycle, HEATERS_MAX_DUTY_CYCLE );
-    dutyCycle     = MAX( dutyCycle, HEATERS_MIN_DUTY_CYCLE );
+    F32 deltaTempC    = targetTemperature - currentTemperature;
+    F32 capDeltaTempC = MAX( deltaTempC, HEATERS_ZERO_DELTA_TEMP_C );
+    F32 dutyCycle     = sqrt( ( WATER_SPECIFIC_HEAT_DIVIDED_BY_MINUTES * capDeltaTempC * flow ) / PRIMARY_HEATERS_MAXIMUM_POWER_WATTS );
+    dutyCycle        *= heatersStatus[ DG_PRIMARY_HEATER ].heaterEstGain;
+    dutyCycle         = MIN( dutyCycle, HEATERS_MAX_DUTY_CYCLE );
+    dutyCycle         = MAX( dutyCycle, HEATERS_MIN_DUTY_CYCLE );
 
     return dutyCycle;
 }