Hi all - let me preface my problem below by saying I’m a fairly new homeowner, and don’t really know much about vinyl siding. I suspect I’ve done something wrong, but I’m not really sure where I went astray:

I recently had to remove and then re-install a pre-hung entry door leading to our 2nd story deck. The original installation had a plywood “plate” under the exterior sill (between deck lumber and bottom of frame/door threshold), which was wicking water up to the plywood subfloor and framing members. After removing the door jambs, I unlocked (and pulled nails from) several panels of the vinyl siding around the door frame so they could be held out of the way. I pulled a bunch of nails out of the existing J-channel, so as to get flashing underneath it (didn’t completely remove it though). I put aluminized flashing tape around the exposed parts of the subfloor and framing members (about 2’ up the framing members, tucked under the remaining plastic vapor barrier). I re-installed the door, screwed the J channel back into the framing members, and re-attached the siding panels. I replaced the plywood plate with a piece of ledger board flashing and sealed everything up with silicon. Finally, I filled in the (small) gap between the J channel and brick molding with silicon.

It rained all day yesterday, and I discovered the subfloor had become wet around the frame. It looked like the water was coming in where the vertical framing members (both sides) meet the subfloor. Not exactly the same spot water was getting in before. The only thing I can think of is that water is getting behind the siding (and apparently behind all the flashing tape). Did I overlook something when reassembling the exterior/siding? Should I have pulled all the J channel off and reinstalled it after the door was in? Any thoughts are appreciated…

Thanks,
Andrew

Check the j-channel on top of the door so water isn't draining from the channel between the side j-channels and the door frame.

Usually the top j-channel will have "taps" cut and then bent over into the side j-channels so water drains from the top j-channel down into the side j-channels.

Also make sure the bottom of the side j-channels have an obstruction free exit point so water drains and doesn't collect were it shouldn't at the bottom of the door area.

It is possible the old leak was due to the J-channel not being installed as described. It is also possible something is wrong higher above and the water is running down until it finds a way in.

Note, do not nail vinyl down solid. It needs to slide around to accommodate expansion and contraction.

Thanks, guys. I took a close look at the top of the door, and it doesn't have J channel. It looks like some sort of aluminum flashing. Anyway, I'm going to "peel" back the siding again to try and find where the water is getting in. While I'm at it, I'll replace the aluminum piece with J channel, cut per skiberger's recommendation.
Chances are good this door has always been a pain. There is a gutter above it, but the door and side of the house still get pretty wet during windy rain storms - no overhang to shelter it, and a lot of spashing from the deck (only about 4" below the door's threshold).