Answer: This problem is caused by a failing or failed breath transducer.  You should first read the article on "Breath Creep" to understand a little more about the breath transducer itself.

If you remove the access panel on the top part of the EWI1000 you will reveal the breath transducer.  This transducer or "breath block" as Nyle refers to it, is very suseptible to corrosion from moisture entering the chamber.  Methods for reducing moisture entering the chamber are discussed in some of the other questions here including the one mentioned above.  The breath block usually fail in the fashion described in this question and the easiest and sometimes only method for repair is to get a replacement breath block.  Breath transducers are available from IMC.  Nyle Steiner also makes his own breath transducer which I think are somewhat better than the Akai.  Installing the Akai is a snap, you simply remove the old one and replace it with the new one and make two small and very obvious solder connections.  Installing a Steiner breath block is similar although you must solder a resister that he supplies in line with one of the connections. 

Inside the breath transducer a membrane not unlike a speaker membrane with a metal center plate senses the breath intensity and is being pushed up toward the green lid that bears a bipolar contact plate. When air is blown into the tube the vibrating membrane is pushed up to the lid and causes alternating contact between the to poles. One method you can try before replacing is loosening the screws that mount the green lid on the top of the breath block.  Sometimes this will free up some space and allow the membrane to expand and contract correctly  After reassembling everything and confirming that it's working, be sure to seal the edge around the top of the breath block with caulk or silicone sealant so that moisture does not enter the breath block and corrode it.