Very often in change of the weather, the doors being wooden or plastic uPvc doors can make the door hard to open due to pressure on the locks. As wood and metal parts expand and shrink due to temperature change. So if you find it hard to open the lock, wait for the weather to change or try to pull the door in different direction to see if it gets less pressure, but in all cases do not put pressure on the keys as they may snap.
If the lock does open when the temperature changes, then at least you know that when calling a locksmith you safe on parts which can be expensive especially when it's uPvc doors as they have mechanism strip operated by a gearbox.
For all your locksmith needs, you can contact us at Max Locksmith.