As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
YYC - FLIGHT 2335 - THE FLIGHT RETURNED TO FIELD AFTER THE CREW RECEIVED A FLIGHT COMPARTMENT AND CABIN DUCT HOT CAUTION LIGHTS. THE DUCT TEMPS WERE NORMAL. CABIN WOULD NOT PRESSURIZE AFTER CYCLING THE AUTO AND MANUAL BLEED SWITCHES. MAINTENANCE INSPECTED THE AIRCRAFT AND CLEARED THE MESSAGES IAW Q-400 FIM. MAINTENANCE WAS UNABLE TO DUPLICATE THE WRITE-UPS WHILE PERFORMING THE OPERATIONAL CHECKS. THE AIRCRAFT WAS RETURNED TO SERVICE.