What was found
GEG ON FLIGHT 2355- AFTER SELECTING AIRFRAME DEICE BOOT SELECTION TO FAST, RECIEVED DEICE PRESSURE MASTER CAUTION. RAN EMERGENCY CHECKLIST, NO ABNORMAL DEICE PRESSURE INDICATED ON EITHER SIDE. NO.5 GREEN LIGHT ON OVERHEAD DEICE PANEL ON FIRST OFFICERS SIDE STAYS ON AFTER IT SHOULD GO OUT. NO.6 GREEN LIGHT CAME ON AND NO.5 LIGHT ON FIRST OFFICERS SIDE STILL STAYS ON GOING TO SLOW OR MANUAL DOES NO GOOD. REMOVED AND REPLACED NO.5 DUAL DISTRIBUTION VALVE. OPERATIONAL CHECKS GOOD. AIRCRAFT RETURNED TO SERVICE.