Index: firmware/App/Modes/ModePreTreat.c
===================================================================
diff -u -rc1b9ac0dbf2196280895d2e440dd7ac288ac8424 -rd521a5bf7b77afeaf2b5593f8c287591cda3385c
--- firmware/App/Modes/ModePreTreat.c	(.../ModePreTreat.c)	(revision c1b9ac0dbf2196280895d2e440dd7ac288ac8424)
+++ firmware/App/Modes/ModePreTreat.c	(.../ModePreTreat.c)	(revision d521a5bf7b77afeaf2b5593f8c287591cda3385c)
@@ -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;