2 years ago? When you originally did the job were you intending to provide a perpetual warranty? I can't see a business reason to do this for free; if you're trying to keep a potential repeat or future customer happy, it's on the cuff. What is your plan of action if you find that your original work was fine, but the HO did something that fouled it up long after your original warranty expired? I'll be surprised if you get any money out of this.
