As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER PUSHBACK AND ENGINE START FA'S IN AFT GALLEY REPORTED A STRONG BURNING ELECTRICAL ODOR FROM THE AFT CENTER LAV AREA. FLIGHT RETURNED TO THE GATE AND DEPLANED. LAVATORY WASTE SYSTEMS VACUUM GENERATOR. C/W MSI PREVENTION PROGRAM STEPS A - G FOUND VACUUM GEN CB POPPED IN REAR CB PANEL FWD VACUUM GEN TO MEL 38-30-01D "M" PROCEDURES C/W MEL & PLACARD INSTALLED. (LP: 8081427)