The FCOM procedure on a normal start is after a successful start if the edge start switch does not go to Auto/OFF from GND then manually turn it to that position.
Why then is there a reference NNC for Start Valve Open which has the first item as Engine Start Switch Auto/OFF?
2 separate problems, one of which has a symptom that might look 'similar'
Engine start switch didn't move to auto/off. The switch is being restricted (not uncommon with age) from moving to the auto/off position, but otherwise, its no longer actually doing much (no other lights, etc).
Start valve open means there is a valve still open which should have closed. is it being commanded open? or is it stuck?