Hi John,
We had these i the NICU/SCBU at Leigton Hospital In Crewe. I never encountered an error 33, plenty of 51,53 which relates to the O2 Cell.
If your really stuck I know the EBME guys there have a manual, I am sure if you give them a call they will check the manual for you.
If you ask for Andrew or Mark, they are very helpful guys.

Direct Dial: 01270 612234

Best Regards

Dom