Symptoms
- Keys rise back slowly after you release them, sometimes only partway
- Fast repeated notes fail or sound uneven
- The keyboard feels heavier than it used to
- The problem is worse in humid weeks or after the piano stood unused
Likely causes
Humidity and swollen wood
Moisture swells the key bushings and the wooden parts of the action, increasing friction everywhere at once.
Tight centre pins
Each hammer, wippen and damper pivots on a tiny pin in a felt-lined hole. When the felt swells or gets dirty the part moves sluggishly and drags the key.
Weak or misadjusted springs
Uprights rely on small springs to return hammers and dampers. On grands, the repetition spring needs correct tension for fast repetition.
Worn or neglected action
Compressed felts, dirt and decades without regulation make an action slow and uneven.
What you can safely check yourself
- 1Check the humidity with a hygrometer and bring the room to 40-50% for a week.
- 2Test every key slowly and mark which ones are slow; note whether they are grouped together.
- 3Play the slow keys after the piano has been used for a while: if they improve with playing, friction is the likely cause.
- 4Make sure nothing on the music desk, lid or fallboard is resting on the keys or action.
What not to do
- Do not oil or spray the action; pivots are felt-bushed and lubricants damage them.
- Do not bend springs or adjust screws in the action without training.
- Do not leave the piano unused and closed in a hot, humid room for months.
Quick fixes vs. call a pro
You can usually handle it
- Controlling humidity in the room
- Playing the piano regularly
- Mapping which keys are slow
Call a technician
- Keys still slow in dry conditions
- Repeated notes failing on a grand
- Whole keyboard feels heavy and uneven
- Hammers or dampers moving sluggishly
What a technician will do
A technician eases the key bushings, frees tight centre pins, checks springs and, where needed, regulates the action so every key returns evenly. A few keys can be done in under an hour; easing and regulating a whole action is a larger job of several hours, sometimes over more than one visit.
A piano holds about 18–20 tonnes of string tension. If a fix means opening the action, turning tuning pins or working near the strings, leave it to a technician.
In Israel
Pianos near the sea and in ground-floor apartments in Israel tend to suffer from slow keys in summer. Running the AC's dry mode during humid months helps a lot.