If the fan and light is working but no heat then its more then likely the heater element in there at fault.
What you need to do is empty the oven and remove the back panel inside the oven.
There you will see the heater element around the fan blade.
Check this and see if theres any signs of burning on there. If so then you can replace it from there.
If it looks ok then you need to remove it and test it with a multi meter and replace from there.
So check the heater element at the back of the oven inside and im sure you will find this will be the heater element at fault here.