Pianos are a collection of hundreds of moving parts. Keeping these moving parts working is the function of regulation. When parts stick, jam or break, repair work is needed. Repair work involves replacement or repair of existing parts, keeping the piano in original condition.
Most repair work can be done in the home, however major replacement work such as repining and restringing, fall under the restoration category and should be preformed in a fully equipped piano repair shop. I would more than likely make a referral for repairs that may require a shop repair or would do the work myself in a shop that is already established.