Humidity – Pianos are constructed largely from wood which is susceptible to expansion and contraction with changing temperature and humidity conditions. This can cause problems for example:
If the environment is too humid, action bushings can cease up causing sticking notes. This can be cured if it is not too advanced, and I would do this as part of a normal tuning. If it is more pronounced, I will recommend installing called a “Piano life saver system” by Dampp Chaser. I carry these and can install them, they are a small 15w heater which gently brings the humidity level inside the piano down. They are not expensive to keep running as they are only 15w and will make a big difference in damp environments. Most churches have them! Humid conditions also often cause the piano to go sharp tuning wise, due to the swelling of the plank.
Problems also occur during the winter time when central heating comes on. This creates a very dry environment causing the plank to ‘relax’ and loosen it’s grip on the wrest pins that hold the strings. The result is that your piano may go out of tune, sometimes quite drastically if the piano is of a certain age. Of course, tuning can help here, but prevention is better than cure in this instance. I sell devices that hydrate pianos that can be soaked in the bath periodically. An alternative solution which can save on purchasing one of these is to fill jars/ice cream tubs with water and keep them in the bottom of the piano, topping them up once a week.