What does F53 mean

I live in Spain and just bought the Indesit oven (1 Week) and on a whole I am pleased.However I used it last night turned it off and the cooling fan came on as normal (how loud is that fan !!!!), and then it went off I assume as it was not running later. I woke this morning with this humming noise in my house... the fan on the oven. It was blowing out very cold air and showing F53.. It had locked up the door and that damn fan was driving me nuts blowing out cold air. In a moment of inspiration I turned off the electric to the house which seemed to reset the oven which is working perfectly fine again. I really do not want to go to the shop, customer service here in the Canaries means a lot of complicated explaining in Spanish and finally they send things away to be repaired which could mean I am without t for long time (nothing ever gets exchanged here even if you only had it for one hour). Should I be worried about this F53 and what does it mean. I may have not turned the knob completely round to off because the shadow from the work surface means you cannot read it with out a torch (very bad design) as the contrast of the writing against the knob makes the black writing vanish.