First check if you have assembled the breastpump correctly and make sure that there is no kink in the tube.
If you are using the SCF332 with batteries, replace the batteries according to the instructions in the user manual.
If you are using the SCF334 or the SCF332 on mains electricity, check to make sure you are using the adapter that was supplied with the product.

If the problem persists, contact consumer care via www.philips.com/support.