The (bass) keys of the upright piano are stuck. How to fix it DIY.

[themaximillyan]

• In the video, it's clearly visible that the reason the key is sticking is due solely to excessive room humidity. Initially, the keys swelled from too much moisture, then dried out and, as a result, their geometry relative to each other was altered.It's also noted that the hammers are working normally there, which rules out the possibility of a sticking hammer.
  
  Steps to repair this issue are as follows:
  
  1 Key Removal: Start by carefully removing the affected piano key from the upright piano action, holding the key in your left hand.
  
  2 Tool Preparation: In your right hand, use a medical pair of tweezers with closed jaws.
  
  3 Reshaping the Keyhole: Insert the tweezers with closed jaws into the keyhole where the 'front rail key pin' usually fits during the piano's operation, and gently rock them side to side. This will slightly widen the shrunken keyhole, restoring it to its original smooth, fabric-like state.
  
  4 Reinstallation: Place the key back into the piano keyboard. It should no longer rub against neighbouring keys and should function correctly.
  
  5 Drying Process: For improved key stability in the future, it is recommended to allow the entire keyboard to dry for several days, even suggesting the temporary use of rice to aid in drying. Additionally, wiping down the key pins ('the front rail key pin' and 'the balance rail key pin') and the metal 'capstan screw' with denatured alcohol is good for maintenance.
  
  6 Cautionary Tip: Please note that these tasks should be undertaken with carefulness. If you lack experience, it's advisable to seek professional assistance so as to avoid causing damage to your upright piano.
  
  7 Occasionally, the cause of a stuck key may be the 'front rail key pin' itself. In such cases, it can help to gently rotate the pin itself, which may have shifted position. The pliers might come in handy to adjust the position of the side of the 'front rail key pin' relative to the keyhole.