Lost root when phone rebooted - can't get to download mode only Android system recovery I have had my phone (Samsung Galaxy S4 GT-I9505, Android 4.4.2) rooted for a while (can't remember exactly how I did it now) but last night I exhausted the battery and when I charged and powered back on I had lost root. SuperSU quits with error message "There is no SU binary installed and SuperSU cannot install it. This is a problem!"

I have tried to re-root following these instructions but when I do the Volume Up + Centre Home + Power combination I don't get the warning message about installing custom OS, instead I get:


  Android system recovery &lt;3e>
  
  KOT49H.I9505XXUFNA5
  
  Volume up/down to move highlight; power button to select.
  
  
  reboot system now
  apply update from ADB
  apply update from external storage
  wipe data/factory reset
  wipe cache partition
  apply update from cache
  
  
  [Exposed Android with red warning triangle]
  
  # MANUAL MODE #
  
  -- Applying Multi-CSC --
  
  Applied the CSC-code : BTU
  
  Successfully applied multi-CSC


Now from here I don't seem to be able to flash TWRP because nothing shows up in Odin when USB is connected. If I select "reboot system now" I get back into un-rooted Android (annoying because I make extensive use of multiple profiles on Titanium Backup); if I select apply update from ADB then the S4 then appears as a device when I run adb devices:

List of devices attached
6496ea42        sideload


But still nothing on Odin.

Can anyone advise how I can re-flash TWRP and re-root?

Many thanks

Tristan
On the Samsung Galaxy S4 (GT-i9505) Volume Up, Power and Home is to enter recovery mode. Volume down, Power and Home is to enter 'Download Mode'. From download mode you can make the device visible to odin. From Odin you can flash a custom recovery, or root the device with CF Auto Root and other methods such as flashing a pre-rooted stock ROM for example. 

If your device shows as not being rooted, when previously it was and you have not unrooted it manually, this could be an issue with the SuperSU binaries, and sometimes installing these via the app, or via the 'recovery' option within the app can fail. You can download the SuperSU zip from Chainfire and flash it in a custom recovery. 

Generally the safest bet is to backup anything you need, flash the Stock ROM through Odin, and root, or flash a pre-rooted stock ROM. Then you can flash a custom recovery and from that recovery flash whatever you need.