Plumber, plumbing, water heater repair. Upon arrival customer stated that their water heater wouldn’t work but a few mins after lightning the pilot light. Upon diagnosis I found that the intake air screen was dirty. Removed the burner assembly and vacuumed out the combustion chamber, intake screen and underneath where the air comes in. Put burner assembly back in, fired up water heater, waited for 10 mins, and flames are a nice blue color. Set gas valve on B setting. OK now.