What was found
DURING TAXI OUT ATTEMPTED TO START NR 1 ENGINE, N2 ADVANCED TO 26% BUT VALVE LIGHT ON L STAYED ILLUMINATED ATTEMPTED 2ND TIME, SAME ISSUE, ACFT RETURNED TO GATE AND MTX GROUNDED ACFT . MTX DEFERRED NR 1 START VALVE IAW MEL 80-00-2-1 FOR DEPARTURE AND RETURNED ACFT TO SERVICE.