TEFAL PRO FRY OLEOCLEAN : keeps flashing "83" when turned on?

My Tefal Pro Fry Oleoclean keeps going beep and flashing the number 83 on the display when I turn it on. If I keep hitting the hard reset (recessed button at the back) it eventually clears, after a few goes. But the error comes back at the start of each frying session. Sometimes it happens during a fry as well. The number is not listed in the manual, and I can't find anything relevant online. Of course, this happened just after the guarantee expired.