As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
THE CREW REPORTED, DETECTED A STRONG ELECTRICAL BURNING ODOR COMING FROM THE LAVATORY AREA. MAINTENANCE RAN THE AIRCRAFT ENGINES AND DID NOT NOTICE AN ODOR UNTIL THE BLEED AIR WAS TURNED ON. THE ODOR WAS DETERMINED TO BE COMING FROM HOT BLEED AIR ON NEW DUCTING. OPERATIONAL CHECKS WERE GOOD, AND THE AIRCRAFT WAS RETURNED TO SERVICE.