a lot of reported faults lately appear to be related to the  VERY VERY COLD weather,this is  causing FREEZING in  the condensate pipe.
 check  that you pipe is not frozen 
try thawing the plastic pipe out with kettles of hot water or  a hair dryer.  
more insulation on the pipe is needed. increase  to the next size of pipe over the existing pipe when the weather improves.
                
 wirecutterman
                
 January 2010