Check for signs of wear & tear.. Avent's motor is quite lasting... Maybe just need to change the spare parts. Check the valves for years.
Alternatively go to the service centre for a replacement - the pumps are usually under 2 years warranty
Like what Roshni mentioned, it should be covered under Philips's 2 year warranty. You can contact them to find out more about how to you go about sending yours for repair:
http://www.philips.com.sg/c-w/support-home/support-contact-page.html
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