Is a plumber or builder responsible for extensive damages incurred for faulty plumbing installation discovered 7 years after house was built?

From your description, it sounds like your claim may be barred by Colorado's statute of repose. With respect to claims for defective construction, C.R.S. sec. 13-80-104 states: "in no case shall such an action [i.e., a claim for defective construction] be brought more than six years after the substantial completion of the improvement to the real property." The statute does provide that if the claim arises in the fifth or sixth year after, the claim must be brought within two years of when you knew or should have known of the manifestation of the defect. If you do not know of the manifestation of the defect until seven years after substantial completion, the claim is probably barred. That said, for a claim exceeding $8,000, it may be worthwhile to consult with a plaintiff's construction defect lawyer to walk through the specific facts and dates pertinent to your situation.