When the operating (moving) sliding patio door closes and locks, the other end should interlock with the stationary door (fixed panel) to seal out wind and drafts just like with the doors you can buy and get installed with help from experts at https://bi-folding-doors.co.uk/. You can contact door company Brownhills to learn more.
There can be several reasons why this interlock may not perform as designed…
1. The weather seal has worn and needs to be replaced.
2. One of the doors, usually the operating door, is warped.
3. The stationary door (fixed panel) has moved away from the jamb slightly and does not allow for a good seal at the other side where the doors interlock.
4. The width opening for the sliding door system may have been sized slightly too small during installation, usually by a 1/4″ – 1″, which prevents the operating door from having enough room to close far enough to interlock with the stationary (fixed panel).
The solutions are as follows:
For #1, The operating door needs to be temporarily removed so that the weather seal can be replaced.
For #2, The same as above, but oversized weather seal material needs to be used.
For #3, The fixed panel needs to be re-set in the jamb and secured.
For #4, The fixed panel needs to be removed and the jamb side planed (shaved) down the necessary amount for the doors to seal.