I have a Canon IPF765 that was working at a previous site but is showing error codes after being moved. After googling 1 suggestion was that it could be air bubbles in the ink lines, so I've checked and that is the case. I know I need to run a print head clean to force ink though, but can't get the device into service mode. I hold Navigate and Load while starting it up, and the s appears in the top right indicating service mode, but it still just goes straight back into the error state. The only thing I can access is a general information menu.

I've tried several times and tried everything I can think of such as holding the buttons for the full restart, releasing them as soon as I see the S, leaving it powered down for 15 minutes etc but same result every time. Does anyone know how I can get this into service mode or another way to sort the issue?