Q&A: Is My Pump Broken?
If your pump is suddenly unable to drain your breasts, check it over for weakened or faulty parts. Is something wearing out (like a valve or membrane)? Are there any cracks? Is anything loose? If so, the manufacturer should be able to give you the information you need to find replacement parts. Check its website, or call the number listed in the printed instructions that came with your breast pump. If you aren't sure if it's working, put a flange (the part that goes on your boob) against your cheek and turn on the pump. The suction should be strong. (It might even hurt a little.)
If the pump is new and is simply too weak to be effective, return it and get a better one. If you've had it a while, a part might not be working properly because it's gooped up with dried milk. Soak any dirty parts in vinegar for a few hours before washing. (This is another reason it's so important to wash the parts that come in contact with your milk in warm, soapy water each time you use it.)
Lastly, make sure the problem is with your pump and not with your ability to let down in response to the pump, your milk supply, or your expectations of pumping. (It can be normal to get as little as a half-ounce or so from a breast, particularly if you are pumping between feedings. Here are some ways to pump more milk.)