The question is written more in code than in plain language - and there is no mention of make or model which often helps.
So the fan oven did not heat...
But some element did heat up (not in the fan oven presumably)
But did this element heat up when it should have done so or did it get hot when it should not have?
A selector was faulty
The fan oven began working when a wire was moved to a different terminal - a diagnosis was made of a defective selector.
A new selector was fitted with (apparently) identical wiring but now nothing heats up but the fan does run.
The old arrangement was tried and then the new one and this was repeated twice more but the symptoms remained the same.
Simon fears insanity.
My judgement is that the replacement selector is not identical to the defective one - OR - wires are being inserted into the wrong terminals.
A continuity test to each load and an understanding of the selector connections might help solve the mystery.
Good luck...
Peccavi
January 2013