zanussi electric cooker fan not working ,not gaining temperature?

model number zce7690x.my cooker has two ovens top one working fine so is grill and hob.The main oven light comes on you can hear a much quieter sound from the fan but it is not reaching temperature and the oven is only warming slightly.This happened late last night, we have eight guests coming for lunch on Sunday, please advise? The cooker is 3 years old