UPVC is widely used for doors and windows in homes across the UK because it is tough, maintenance free and has a long lifespan. However, UPVC products are likely to respond to high temperature changes more dramatically than other materials such as timber and aluminium. As a result, during the warmer months you might experience your UPVC doors and windows becoming stiff and difficult to open and close due to the UPVC expanding under the heat.
This is perfectly normal and dark UPVC products are often affected more due to dark colours absorbing the heat. It is nothing to worry about though, your products will sort themselves out once temperatures drop. When the sun sets, your windows and doors will retract returning to their normal size and position.
To cool down your UPVC doors or windows, spray the outside with cold water, or wipe it down with a cold, damp cloth. This will help it to shrink back to size and work as normal.