This is a question I have heard too many times to count.  My answer would be, at
least once a week, if not more!  Alright, back to reality. To answer this question
without prejudice I will simply quote what your carpet manufacturer has to say.
After all, they did make your carpet and are the ones responsible for the
warranty. Shaw is the largest manufacturer of residential carpet in the world.
Periodic professional cleaning of the overall carpet is required. The frequency of
overall cleaning may vary depending on the level and type of traffic and the
conditions to which your carpet is exposed. This may range from as little as 6
months to 24 months between cleanings. Your carpet must be properly cleaned at
least once every 24 months to maintain your warranty.

Shaw recommends only Hot Water Extraction utilizing carpet cleaning products,
equipment, and systems certified through the Carpet and Rug Institute’s Seal of
Approval Program. These products are listed at Warning:
Non-Approved cleaning products and topical treatments, applied by you or by a
professional carpet cleaner, will void your warranty.

Shaw residential warranties require that professional service be performed by an
IICRC Certified Firm.  We recommend  Dave Steely , Maximum Carpet Cleaning
in Concord. As we believe he works harder and does a far superior job than any
other carpet cleaning company we have ever worked with.  Well, that might not
be written in their warranty but it should be.

Now you know.  I wish I could educate everyone on the proper care and
maintenance of their carpet, but for now I will have to settle for my clients only.  
I have often said that if people knew the proper steps to maintain their carpet ,
most would follow them.  Unfortunately most people do not. Even when you
purchase new carpet you can get wrong information from your salesperson.  The
one key thing to remember, when in doubt Contact Me.  You can always email, or
call me with any questions or concerns regarding your carpets.  I will be happy to
answer them. I can even help when you are purchasing new carpet.  
By working together to maintain your textiles we both win.
Proper maintenance is the key to longevity.  
(925) 429-3800