I experienced extreme wrist pain for a period in college. I was learning Rachmaninoff's 1st Piano Concerto at the time and some other crashy romantic pieces like Liszt's 10th Transcendental Etude. The pain got so bad that I could hardly stand to turn a door knob after a practice session. My teacher was smart enough to pull back on my work load and give me a chance to recover. In hindsight I think I was practicing with WAY too much weight and stiffness. I was using weight to try to get more clarity and volume on broken down Yamaha G1 practice pianos. What I wound up doing was over stressing my wrists to the point of pain. Wrists can only take so much. Even in big chordal passages you need to make sure to not overplay the piano - that is, don't try to generate more volume than the piano is capable of. Find places to hold back on the volume so that you aren't playing FFF the entire time (this is easier on the listener as well). And make sure not to continue to put pressure on the after the note has sounded - this wastes useless energy and puts a LOT of stress on the wrists. Also, try to keep your wrists up - don't let them sag down below the level of the keys. This puts your hands at an angle to your forearms, which also puts a lot of stress on your wrists. It's ok for the wrists to be higher than your forarms, this is part of having flexible wrists, but the wrists really should rarely or never go below your forarms. Again, this generates a lot of stress.
Another thing, do not practice for too long in a row - 15 to 20 minutes at the most for demanding music. One of my problems was that I was practicing far too long without a breat - 2 to 3 hours. Most of it was not very productive either, because I went unconscious part way through
Hope this helps. Good luck with it...