My Philips Avent breast pump is leaking

Check if you have pressed the assembled pump body against your breast correctly.
Making sure that your nipple is centered, so that the massage cushion creates an airtight seal.

Leaning too far forward or backward, while using the breast pump can result in leakage around the rim between the pump and the bottle. In order to prevent this, position yourself comfortably and somewhat upright (no leaning forward or lying down backwards). It will bring you more comfort, and prevent the breast pump from leaking.

Using the glass bottle with the breast pump can sometimes cause leaking. Switch to the standard delivered bottles or storage cups to express the milk, and feed your baby with the glass bottle if this occurs.