Hi there Peter, Mrs jammyd had a peace lily for several years, and the only flowers it ever had were the ones it had when she was given it. Someone told me that by only watering when the leaves were drooping a lot, the plant (thinking it was going to die) would throw out a flower or two (in an attempt to reproduce I expect).
This worked for us, and last year we had 2 flowers, and the lily was none the worse for it :)
good luck!
jams