neff electric oven?

Hi I have a neff double oven (not sure of the make but found this code on the inside)
E-Nr U1721N2GB 0S FD8405
HBB EP31-7 000322
The top oven/grill are working ok Although the bottom fan oven has no heat, the lights and fan comes on but no heat at all
Ihave instructions for the hob and the extractor fan but unfortunatly not the oven have you any ideas?
Thank you Sharon Ratcliffe