When your top box is delivered, it is done so without any handles on so that the units do not get damaged in transit and to allow you to put the handles on exactly how you want them when your kitchen is fitted.
Once you put the handles onto your door, it does increase the weight of them and as such, you may find that the door does not stay open when open upwards now as the tension of the flap stay friction joint needs adjusting to accommodate for the extra weight.
On page 22 of the technical guide supplied with our kitchens, there is a section that mentions how to adjust the flap stay friction joint
In case you no longer have the guide, here is the information from that guide below.
Adjusting the flap stay friction joint
To adjust the tension of the ﬂap stay friction joint, you will first of all need an allen key.
When you have the allen key, open the top box door to its extent then insert the allen key into the centre hole, as shown below.
Now, turn the allen key to lock the joint open, then turn the allen key back the opposite way to release the joint enough so that when you attempt to close the door, the joint releases and shuts under the friction of the ﬂap stay and soft close mechanism (if ﬁtted).
Now your top box door will stay open until you apply enough downward pressure on the handle to allow the flap stay joint to start closing.