Our house is 15 years old and has double hung vinyl windows. I just noticed that on two windows the vinyl bottom of the top pane (which contains the piece the lock grabs) is sagging downward in the center. So when I shut the lower pane, the matching side of the lock is about a quarter inch below where it should be. The rest of the window frame looks fine. I don't see any gaps on the top of the pane. Just the sagging of that vinyl piece on the bottom.

I am hesitant to strike it upward with a hammer. Is this something that can be repaired? Thanks!

 

The sash needs to be replaced. It may be under warranty, but most warranties don't cover things like that past 10 yrs. Each sash should have all the manufacturers information as well as the detailed info on that sash. Contact the manufacturer or local distributor for help.

 

I don't see any manufacturer info on the window. Where exactly should it be?

 

I've made COUNTLESS service calls to the houses of people 50+ miles away who can't seem to understand how to shut a window. If locks and keepers don't line up, it's usually because the top sash isn't pushed all the way up. So that is the first thing to check. There is usually no need to tap the window with a block of wood and a hammer, usually all you have to do is lower that top sash and slam it back up where it should be.

Occasionally, some wide double hungs WILL actually sag in the middle, and depending on the brand of window and how it was made, tapping the sash extrusion with a block of wood and a hammer WILL correct that situation, at least temporarily. Years ago, we put in some windows made by TTI / Campbell and they had no silicone or glazing tape to hold and keep the extrusions straight with the glass, it was just the friction of the durometer fins within the extrusion. They commonly had the exact problem you describe. Tapping them up and running a fine bead of silicone around the exterior perimeter of the sash seemed to be a good fix... actually the only fix since new sashes are no longer available for that particular brand.

That's the crappy thing about vinyl replacement windows- companies go out of business and the companies that take over often will no longer have parts for their products or stand behind their "lifetime warranty" which for all intents and purposes means the lifetime of the COMPANY, not the lifetime of the window. Pretty sneaky. It's one reason to stick with a good name brand that has been- and is going to be around for a while.

 

The top of the window is fixed and cannot be lowered it also appears fully closed. Are you saying it is safe to hammer up the sagging sash?

 

The term "double hung windows" describes a window where both the top and bottom sash open.

From your last comment, we now understand that you have "single hung windows" where the top sash is fixed and only the lower one opens. If that is the case, then NO, you would not hammer the dividing mullion upward. It has apparently sagged on its glazing- it is probably still stuck to the glass, but since this sagging probably occurred over a long period of time you probably won't be able to just force it back into the correct position. (this often happens when people have fairly wide windows and never lock them, or maybe couldn't get them locked once and then just left them that way, which allows the mullion to sag even more).

You "might" try cutting a stick and wedging that dividing mullion upward to see if you can get it locked. But more than likely, the correct fix would involve removing the insulating glass unit (IGU) from the upper fixed portion of the window so that the mullion could return to its normal position (either by propping it up with a shim/stick as needed or by shutting and locking the window) then replace and reglaze the original IGU so that you basically stick the mullion to the glass back in its original position.