Twice in the last week, I have seen significant soundboard cracks on relatively new grand pianos. Both high quality instruments. This was a Yamaha C3, the conservatory model baby grand.
Why does this happen? In both cases, the pianos had been stored immediately next to heat sources and/or direct sunlight. As heat and sunlight dry out the piano, soundboard cracks are just one of many problems that crop up.
In both cases, I strongly advised the owners to keep their valuable piano away from heat sources and direct sunlight. Thankfully, these soundboard cracks are not significantly impacting the tone of the piano yet. If the pattern continues though, pianos stored in environments like this may lose decades of useful life.
If you have a piano, particularly a high quality one, know what’s good for it!