Index: firmware/App/Modes/ModePreTreat.c
===================================================================
diff -u -r66e748932d4d47b275d7763cf828602bce492b1b -r68ad3f72e0e99411960c27f50cbec9e2dd797a4a
--- firmware/App/Modes/ModePreTreat.c	(.../ModePreTreat.c)	(revision 66e748932d4d47b275d7763cf828602bce492b1b)
+++ firmware/App/Modes/ModePreTreat.c	(.../ModePreTreat.c)	(revision 68ad3f72e0e99411960c27f50cbec9e2dd797a4a)
@@ -997,6 +997,12 @@
 {
     HD_PRE_TREATMENT_PAT_CONN_STATE_T nextState = PRE_TREATMENT_PAT_CONN_WAIT_FOR_UF_VOL_STATE;
 
+    // Look for cartridge door to open (indicating user inverting dialyzer)
+    if ( STATE_OPEN == getSwitchStatus( FRONT_DOOR ) )
+    {
+        doorOpened = TRUE;
+    }
+    // If UF volume set by user, move on to next state
     if ( TRUE == setUFVolStatus )
     {
         setUFVolStatus = FALSE;