Lots of things can play into a stuck sparge:
- If 5% or more of the mash is flaked or rolled barley, wheat, corn, oats, rye, or there is a lot of sticky malt types such as Spelt malt, then rice hulls MUST be used.
- If the grain crush is too fine, or the mash temperature is too high - it can happen with ANY malt
- Doing too much vorlauf, which over-compacts the grain bed
- Using a pump (especially in RIMS setup) which can REALLY compact the grain bed.
- Sparge water that is hotter than 170 degrees
This is a link to a pretty good article on the subject:
It is 18 years old, but still holds true today!