As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
HOT ELECTRICAL ODOR COMING FROM THE CABIN. ODOR STARTED AT FL100 AND CONTINUED TO GET WORSE. CREW TURNED DOWN THE HEATER CLOSED FOOT WARMERS, PULLED COFFEE POT OUT OF SLOT. ODOR DID NOT STOP. AT FL180 TO FL200 CREW MADE DECISION TO RETURN TO CLT ON DESCENT BEGAN TO QUIT AT FL100. ODOR WAS GONE ON THE GROUND.