If we take a look at the Flash infusion, it says that whoever is hit by your blast must make a Will save or be blinded for one round.
Element(s) fire; Type substance infusion; Level 4; Burn 3
Associated Blasts blue flame, fire, plasma
Saving Throw Will negates
Your kinetic blast is so bright that it blinds your foes. Whenever an infused blast hits a foe and penetrates its spell resistance, that foe must succeed at a Will save or be blinded for 1 round, regardless of whether it takes damage from the blast. You can reduce the blast’s damage by half to increase the DC of this save by 2.
This would make you think that yes, everytime you take a hit (no matter if the damage was reduced to 0), you must roll your Will save or be blinded for one round.
However, there is this exception on the Infusion ability's text:
When a kineticist modifies a kinetic blast with a form infusion and a substance infusion that both require saving throws, each target first attempts a saving throw against the form infusion. If a target succeeds and a successful save negates the infusion’s effects, the entire kinetic blast is negated; otherwise, the target then attempts a saving throw against the substance infusion.
So, we have to check which saving throws are allowed by the Wall infusion, since it is a form infusion:
Element(s) universal; Type form infusion; Level 5; Burn 3
Associated Blasts any
Saving Throw none
You create a wall of churning elements, flensing debris, or roiling energy. The wall appears within 30 feet and can be either up to 10 feet high and up to 120 feet long or up to 20 feet high and up to 60 feet long. All creatures and objects in one of the wall’s squares when you create it take 1/4 the normal damage from your blast with no saving throw (or half the normal damage for an energy blast).
Anytime a creature crosses the wall, it takes half the normal damage from your blast (or full damage for an energy blast). The wall is not completely solid, but it does provide cover against attacks from the other side of the wall. The wall lasts for a number of rounds equal to your Constitution modifier or until you use a wall infusion again.
We see that there is no saving throw allowed to negate the wall's effect or damage, thus, the only saving throw allowed is that from the Flash infusion, to negate the blind condition.
Do note that using both infusions incur on a 6 Burn cost, which is really expensive, and that your maximum burn per round is limited by your kineticist level:
A kineticist can accept only 1 point of burn per round. This limit rises to 2 points of burn at 6th level, and rises by 1 additional point every 3 levels thereafter.
In other words, you are looking at an (unmodified) level 18 to be able to pull this off. Of course, with the Gather Power ability, you can reduce this by 3 levels for each move action you spend reducing the burn cost of your blast, up to 3 points. At 5th and 8th levels, the burn cost can also be reduced by another point, which reduces the minimum level to blast a flashing wall of fire to 6th level. So you will not be able to use both infusions by the time you acquire both abilities (5th level).
- At 6th level your maximum Burn is 3 points (reduced by 1). So you must gather power to reduce 3 points of burn here, a full-round plus a move action.
- At 8 level your maximum Burn is 4 points (reduced by 2). You have to gather power to reduce 2 points of burn, so at least a full-round action.
- At 9 level your maximum Burn is 5 points (reduced by 2). Gathering power once is enough here.