Doorwall leaks can be tough. A customer said that after he installed a door wall off his kitchen, some water ran the wood under the door after a heavy rain and into the basement but couldn’t pinpoint the source.
First I ask if you used flashing for the doorwall above and below the doorframe? With a brick house, it may be a little difficult to flash the top, so a high quality caulk could be key there. Prior to installing the door I install a metal flashing from under the door, about three inches, so it hangs over the exterior wall about one half of an inch.
I caulk between the flashing and the sill, extensively, (remember you will never get there again) then caulk between the threshold of the door wall and the flashing. A lot of water will be flowing off the door wall and onto the gap below, so don’t leave a void for water to seep into.
Then, as with the top, the sides have to be caulked properly. Try to get at least as much caulk into the void because it is wide. Too often installers get a thin skim coat of caulk to cover a void. The problem is as soon as there is any settling or expansion the caulk will get hairline cracks. Soon afterward dampness, mold, pealing paint, and other problems may become apparent inside the house. This is especially important with dissimilar surfaces as with wood or vinyl against brick.
One way to help seal the door wall to the brick house is to use non-expanding foam sealant. Usually I try to install the foam deep into the void so it is touching the backside of the exterior casing. My goal is to stop the water, and the drafts, at the source. Don’t let the water get past the first quarter inch, why fight something after it gets in the void.
Also, check the threshold on the door wall. It could have drain holes that are plugged or facing the wrong direction.
Did you caulk the side jambs of the door wall to the threshold? Water could be seeping there.
Last but not least, get some Silox sealer, and paint the exterior two or three inches of the brick around the door wall. Seepage could be through the mortar. Paint the perimeter in a neat line so if it leaves the bricks darkened it won’t look messy. If it works you could seal the whole back wall.