Jonesy, there could be a number of reasons for this but as long as the shrub looks generally healthy, I don't think you need worry. Pyracanthas flower on one year old wood, so a hard pruning last year could affect the current year's flowering, or even the harsh winter may have had an affect on them.
Pyracanthas are generally forgiving plants that grow in most soil types, they'll flower and berry in sun or shade, but thrive best in full sun. The ones not in full sun may have just had a rest this year. Fruiting shrubs tend to do that for no obvious reason and you did say they'd done well last year.
Originally Posted by: Caz