The button handle has a spring that is roughly cone shaped.
Spring in door handle broken.
Flip the button spring.
To check this you will need to remove your door handle by unscrewing the two screws visible on the internal handle.
A quite odd video for my channel but it shows how to repair something and i m all about repairing old stuff i.
If the small end of the spring is toward the door it may slip into the door hole and bind.
Once the two screws have been removed the handles should just slide away and.
Replacing a door handle spring is really quite simple the only special tool you need is a pair of external circlip pliers.
If your door handle is not returning to the horizontal position it is almost certainly because the spring has broken in either one or both of the handles on the door.
Purchasing replacement spring cassettes.
Repairing the spring in an old door handle.
We have an article that will guide you through measuring and purchasing a replacement door handle which you can view here.
If your upvc door handle is relatively modern then it will likely have spring cassettes already built into the handle which may be broken.