What was found
ON DESCENT WITH THRUST LEVERS IN FLIGHT IDLE NO 2 ENGINE ANTI-ICE WAS SELECTED ON, BUT THE VALVE FAILED TO OPEN, THE BLUE "COWL VALVE OPEN" LIGHT TURNED BRIGHT BLUE, BUT NEVER DIMMED. THE NO 2 ENGINE ANTI-ICE SWITCH WAS CYCLED 3 TIMES. ON THIRD ATTEMPT, THE VALVE OPENED INDICATED BY A DIM BLUE LIGHT. GROUNDED - YES. REMOVED & REPLACED ENG #2 COWL TAI VALVE REF B737-800 AMM 30-21-11, OPS CHECK GOOD.