The main service a piano regularly requires is tuning, this is due to local climate conditions, fluctuations in the temperature, humidity and amount of use.  This should be done at least once a year, however pianos exposed to heat sources, doors and windows that are regularly opened, external walls and heavy use may need to be serviced more regularly, pianos used for concerts and performances are tuned prior to each use.  Regular tuning achieves a higher tuning stability, maintains the resell value of a piano and makes the piano more enjoyable to the player and audience!