I have an insured that purchased a home last spring. Every since he...

I have an insured that purchased a home last spring. Every since he has purchased the home he has had to call a plumber out once a month becuase the sewer keeps backing up. He is now wanting to file a claim on getting this fixed. My thoughts are this is a maintenance issue and not going to be covered by his insurance. Can any of you think of a way that there might be coverage for this gentleman? He has used 4 different plumbers