Is a warranty from a business a contract that must be honored?

2006 replaced sliding glass doors and windows through out residence with up graded insulated glass windows and doors.Company gave a written warranty for 20 years.If glass should fail prior to year 20 -a replacement unit would be provided with no charge.In 11/2012 I noticed filming between panes on one of the sliding glass doors,called company and was told they would order a replacement but the work probably would not be done until the holidays passed. On 01/23/2013 I noticed the other side of same slider was forming same film.Called the company to report new problem 01/28/2013 and find out were the first door was. I was told it'd be best to wait until both pieces came in. 01/31/2013 owner called said unfortunately he no longer had dealings with the company that had manfactured my doors and he really couldn't do any thing for me.My warranty contract states if the products covered are not available a substitute of equal quality or value may be used.