As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: FLIGHT ATTENDANT REPORTED A BURNING RUBBER SMELL AT ROW 22 STARTING AROUND 10,000 FEET UNTIL AFTER LANDING. MAINTENANCE FOUND THE MID LAVATORY WATER HEATER WAS THE SOURCE OF THE BURNING SMELL AND REPLACED IT PER AMM 38-12-16. A SATISFACTORY OPERATIONAL CHECK WAS ACCOMPLISHED WITH NO ODORS NOTED.