If the sliding door and windows in your apartment are not handled correctly you will have problems and they will need an engineer to repair them. You may like to take note of the these instructions on how to operate your door and windows correctly.
Treated with care, they will serve you well and please avoid slamming them when closing since this will shake the frames and glass, causing damage ‐ apart from annoying your neighbours!
If you are unlucky enough to require repairs the following organisation offer this service.
Windows and sliding doors should be regularly maintained. Normally this should only involve a small amount of lubricant such as WD‐40 on the moving parts.
It is also worth noting that on some windows there is a drainage hole on the exterior, at the bottom‐centre of the window, that requires clearing of dirt every so often to avoid rainwater collecting and causing dampness inside on the windowsill. If you note dampness appearing, check these drainage holes first before calling in a contractor.