As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
THE MAINTENANCE TEAM FOUND THE APU BLEED AIR WOULD NOT TURN ON. OPERATIONS WERE CONTINUED PER DEFERRAL BY MEL. THE MAINTENANCE VENDOR TROUBLESHOT AND FOUND THE APU BLEED AIR VALVE WAS DEFECTIVE. THE VALVE WAS REMOVED AND AN OVERHAULED VALVE WAS INSTALLED. OPS CHECKS WERE GOOD. AIRCRAFT WAS RETURNED TO SERVICE.