Index: firmware/App/Modes/ModeDrain.c
===================================================================
diff -u -r9e5ee62245eb2a73b167eabd6c274a71a76a7b0e -r3efd50bef6d3618b9fed1727aa2bc234ededee2a
--- firmware/App/Modes/ModeDrain.c	(.../ModeDrain.c)	(revision 9e5ee62245eb2a73b167eabd6c274a71a76a7b0e)
+++ firmware/App/Modes/ModeDrain.c	(.../ModeDrain.c)	(revision 3efd50bef6d3618b9fed1727aa2bc234ededee2a)
@@ -135,9 +135,13 @@
     // because the initial guess in the heaters driver needs the target flow to calculate
     // the new PWMs for the main and small primary heaters
     setROPumpTargetFlowRateLPM( TARGET_RO_FLOW_RATE_L, TARGET_RO_PRESSURE_PSI );
-    setHeaterTargetTemperature( DG_PRIMARY_HEATER, getPrimaryHeaterTargetTemperature() );
-    startHeater( DG_PRIMARY_HEATER );
 
+    if ( FALSE == isHeaterOn( DG_PRIMARY_HEATER ) )
+    {
+        setHeaterTargetTemperature( DG_PRIMARY_HEATER, getPrimaryHeaterTargetTemperature() );
+        startHeater( DG_PRIMARY_HEATER );
+    }
+
     setCPLDCleanLEDColor( CPLD_CLEAN_LED_OFF );
 
     return drainState;