What was found
(CAN) DURING ROUTINE PERIODIC INSPECTION, DUCT WAS DISSASEMBLED AND TEMP PROBE SCREEN WAS FOUND TRAPPED IN DUCT CHECK VALVE, HOLDING IT OPEN. LOOSE SCREEN REMOVED. VALVE INSPECTED AND FOUND SERVICEABLE. UPSTREAM INVESTIGATION OF MOST LIKELY SOURCE SHOWS PART CORRECTLY INSTALLED. SUSPECT PRIOR FAILURE AND SUBSEQUENT PART REPLACEMENT. NO FURTHER ACTION TAKEN.