To diagnose problems, piano repairers talk with customers and examine the piano's parts. Depending on the severity of the problem, they may replace worn parts, recondition usable parts, or completely rebuild pianos. In some cases, they may reconfigure or redesign parts to solve a specific problem. For work such as regulating, repining, and restringing, repairers use common handtools as well as specialty tools. In addition to repair work, piano repairers may also tune pianos.
Piano tuners increase and decrease the tension of piano strings to tune pianos to the proper pitch.
A string's pitch is the frequency at which it vibrates, and produces sound, when it is struck by one of the piano's hammer. Pianos are tuned with the aid of either an electric or an acoustic pitch reference. The tuner strikes a key and compares the reference strings' pitch with that of the pitch reference. The pitch of each of the other strings is set in relation to the reference string. Modern 88-key pianos have over 200 strings and can be tuned in one to two hours, depending on the condition of the piano.