BOSCH FRIDGE FREEZER ERROR CODE F1

we have an old , but to date very reliable F/F – it is in our conservatory and is used a second unit, our main F/F being in the kitchen . The fridge is used solely to keep drink cool
give some details below
2 days ago i went to get a drink out and found everything frozen solid! it was showing error code F1
nobody had touched the unit for a day or so.
i turned it off and pondered what to do whilst the temperature got back to normal
YESTERDAY morning i turned it back on and it seemed to be operating quite normally at a temp of 6c.The same today
i have now cleaned out all the evaporation water and it still seems to be running fine
there are no unusual noises, just the gentle hum, intermittently as needed, of the compressor, indeed it is probably quieter than our main kitchen unit which is only 3 yrs old.
is this something you are familiar with and do i need to worry or get work done upon it please

unit info
KKU3201GB/05
FD7710
000063

HOPE THIS HELPS – AWAIT YOUR ADVICE PLEASE
THANKS
Chrisjk26