Newell posts can take a tremendous amount of stress, especially if you have kids or folks who really hang on the stair rails for support. To make then really solid they should be attached to the framing with lag bolts or better, carriage bolts that go all the way through from two directions. Systems like the one you describe are destined for failure, one bolt at the very bottom is not going to cut it. (I know that system is common, it's also why most newell posts in new construction wobble.) Here's a diagram of one good way to do it (this person used an attachment plate, I'd prefer bolts to nails, attaching to both the joist and stringer).

Thanks, rwiegand. The problem is that this is a concrete basement floor. Not only that, the floor has radiant heating tubes imbedded in it so I cannot drill into the floor.

post a picture already. A lot of times I route the keylock/lags into the stair caps, runners and/or the face of the newel itself if the stairs structure is built well and I have a solid spot to do so.. with crete floors I may route the keylock into the bottom of solid newel and use a customised redhead into the crete as the keylock lag. Sometimes you have a rickety junky crap stair build and nothing saves the day.

In relation to newel and floor heat. Radiant heat requires perimiter spacing if and when INSTALLED correctly. It should not be under your newel posts and should have a minimum of a few inches space from all perimeters

It took me awhile to get a photo, but here it is:

looks like all the spindles have major gaps. Is your home climate controlled? i have seen keylocks come loose after extreme moisture/dry cycles.

those solid newels? hollow box newals? veneered? im thinkin its attached to the tread . go under the staircase and investigate.( repaoring drywall is cheap if its in the way)

if its a keylock youll need to remove rail@ connector and use a deadblow hammer and a block to tap newel out i say if its a keylock then let us know what you find

I finally got back to this house, removed the loose Newell post, and took some photos.

In the first one, you can see the KeyLock, the lag screw, and the bottom of the post itself. The block of wood is a piece of 2x4. In the second photo, I show the screw in the keylock pushed tightly upward, against another 2x4. You can see that the threads are entirely beyond the wood thickness. I think what happened is that when I complained to the builder a year ago, he disassembled the installation and put a longer screw, not realizing that the unthreaded portion was too long for the application. It seemed tight but shortly it loosened. When it happened again, he said "I don't guarantee my work forever", so I decided to investigate. I screwed the lag screw farther in and it seemed tight, but after a few days of kids going down the stairs, it loosened again. I took it apart again, and came to the conclusion I described above.

I can think of two ways to fix this: find a larger lag screw with larger threads but the same size head, and only 1/2 inch unthreaded part, also the same size, or remove the 2x4 piece and replace it with a new one. Perhaps just a newly installed, shorter lag screw (like the one in the KeyLock link shown in post one, will be tight enough; or put a 1/2" T-nut on the back side of the 2x4 and use a 1/2" bolt. Or, put in a piece of 4x4. One problem is that the old part is glued in so getting it out is tricky, but not impossible, with my tools.

To answer thatsmuchbetter, the post is hollow. I'm not sure what you mean climate controlled - it has heat in the winter, but no A/C

Suggestions?

yes

youve not enuf meat in the hollow newel remove whats there and make a sold block out of 2x materiial IE 4.5x8" tall that fits snug inside the hollow newel glue it in and trim screw it in and attach anew shorter 5" lag and reattach snug

this assumes the keylock is fastened in a very solid blocking &subtread it should work

for the keylock to work both the lag and the mount bravket have to be fully secured into solid blocking (why i asked if you can get under staircase)

Thanks for confirming my analysis. I can get under the staircase but, of course, I can't get under that bottom step, although I can reach it.