Index: firmware/App/Modes/ModeFill.c
===================================================================
diff -u -r6835f89b10dfac6fa12d27b357a85670fdcde088 -rcea079b61dbd17b2ddaec99b1124248147d14e72
--- firmware/App/Modes/ModeFill.c	(.../ModeFill.c)	(revision 6835f89b10dfac6fa12d27b357a85670fdcde088)
+++ firmware/App/Modes/ModeFill.c	(.../ModeFill.c)	(revision cea079b61dbd17b2ddaec99b1124248147d14e72)
@@ -118,8 +118,11 @@
     turnOnUVReactor( INLET_UV_REACTOR );
     turnOnUVReactor( OUTLET_UV_REACTOR );
 
-    startPrimaryHeater();
+    // NOTE: The target flow rate should be set prior to setting the start primary heater
+    // because the initial guess in the heaters driver needs the target flow to calculate
+    // the new PWMs for the main and small primary heaters
     setROPumpTargetFlowRate( TARGET_RO_FLOW_RATE_L, TARGET_RO_PRESSURE_PSI );
+    startPrimaryHeater();
 }
 
 /*********************************************************************//**