The patio wheel adjusting screws are located at either end of the bottom section of the door. Some patio doors have a blanking plug covering the adjustment hole, remove the plug and use a torch to shine into the bottom section of the door to determine where the screw is located and what type of screw it is. There maybe two screws that are visible, one is an adjustment screw and the other is a fixing screw that holds the patio frame together. Use a long screwdriver to turn the adjusting screw in a clockwise direction to raise the patio. Adjust both wheels the same and check if the patio is level by almost closing the door and noting the gap between the door and the frame. Adjust the wheels until the gap is even all the way down. You may need to move the door locking keeper on the frame after adjusting the wheels. If this didnt solve the problem you may need to replace the patio wheels.
Originally, patio doors were all of the French Door variety; that is, a pair of doors that are hinged at the sides and open from the middle, each door pivoting in- or out-wards. French doors are still popular, especially with builders of new homes, as they are comparatively cheap and easy to accommodate in place of windows and offer an alternative evacuation route for families, especially for elderly or disabled people, to meet improved fire safety requirements.
Metal frames, usually aluminium, provide strength in compact form. As notoriously good conductors (which is a bad attribute for insulation), frames made from aluminium are thermally-broken, which is a good attribute. It means that the metals on the inside and outside of the door frames are not joined, preventing the temperatures from being transferred between them. A bare metal frame would look completely unattractive so it is powder-coated in a choice of over 100 standard colours, including a white that resembles pvc.
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