I have had a pair of cockatiels in the past that mated fine and hatched out the babies as though they had read all the books, so I have had some breeding experience albeit only with one pair.
However I now have another of pair that have lived together in the same cage for a couple of years and although they seem to do most of the normal things that cockatiels do before mating they never actually have mated.
The male (3 years old) enters the nest box several times everyday, he also "pleasures" himself on the perches, does the wood pecker impression, whistles his whole repertoire while in the box, does the wing displays and exhibits all the usual signs that he wants to mate.
The female (2 years old) will sit at the opening of the box but has never entered it. She does the tail elevated crouching/peeping position while looking at the male but he seems to take no notice of her in this position.
They both have a varied diet and are in good health generally.
Is there anything that I can do to encourage mating (if you know what I mean)?