What was found
TWO MINUTES AFTER TAKE OFF, RECEIVED AN EICAS AMBER DUCT O'TEMP CABIN LIGHT. REFERRED TO THE QRH EMERGENCY/ ABNORMALS CHECKLIST. AFTER COMPLETING THE CHECKLIST THE DUCT OVERTEMP CABIN LIGHT REMAINED ILLUMINATED AND THE CREW WAS UNABLE TO CONTROL THE CABIN HEAT. THE CABIN WAS EXTREMELY HOT AND A BURNING ODOR WENT THROUGH OUT THE AIRPLANE. DECLARED AN EMERGENCY AND INITIATED A RETURNED TO DEPARTURE AIRPORT. THE CREW LANDED WITHOUT FURTHER INCIDENT AND CONTACTED FLIGHT CONTROL & MAINTENANCE CONTROL. THE TEMP CONTROL VALVE WAS FOUND TO BE HARD FAILED AND HAS BEEN REPLACED.