The piano is a finely balanced instrument, carrying a tension of about 20 tonnes in total. Anything that changes the condition of the parts supporting this great tension will alter the string tensions causing the piano to fall out of tune. Below is a list of the main reasons a piano goes out of tune:
It depends on different circumstances. How often do you play it? Where is piano situated? Generally speaking, the more playing, the more tuning. Pianists, piano teachers, schools and students preparing for piano exams should have their pianos tuned at least 2 to 4 times a year. For learners, amateurs and for pianos rarely played, they should be tuned at least once a year. If the piano has not been tuned for a long time, a pitch raise may be required and subsequent tuning visits required to make the piano stable. For new pianos and newly re-strung pianos, it is suggested they be tuned 4 times in the first year.
If your instrument displays a lack of sensitivity or a decreased dynamic range, it is the time to regulate. There are a list can tell you piano needs regulation.
Your piano may benefit from voicing if some of the following exist.
Professional piano tuning should only be done by a qualified piano technician that has the formal education, experience and high standard.