1. The piano may need more than one tuning to bring it back up to pitch. Your piano is designed to sound its best when tuned to A-440Hz, the international pitch standard. If a piano has gone without tuning for an extended period, its pitch may have dropped far below A- 440. It is impossible to make a substantial change in pitch and end up with a fine, accurate tuning in one step. Instead, a process called "pitch raising" must first be done and only then can the piano be accurately tuned.
2. The piano may go out of tune more rapidly until it has had subsequent tunings on regular basis.
Helpful hints to keep your piano in tune longer.
Start by locating the piano away from direct sunlight, drafts, and heat sources. Excess heating causes extreme dryness, so try to keep the temperature moderate (below 70 degrees) during the winter heating season. et a portable room humidifier, or install a central humidification system to combat winter dryness in climates with very cold, dry winters. If controlling your home's environment is impractical, or if you want the best protection possible, have a humidity control system installed inside your piano. These are very effective in controlling the climate within the instrument itself. Besides improving tuning stability, they help minimize the constant swelling and shrinking of your piano's wooden parts.