A guzheng is not a consumable that has to be replaced every few years, but neither does one purchase last forever. The same instrument played occasionally at home, in a dry and well-ventilated room, and one played four or five hours a day in a studio with wild humidity swings can differ in working life by more than double.
Four things decide how long it lasts. The first is the soundboard: paulownia expands and contracts with every change in humidity, and long spells at either extreme lead to cracks and glue failure — once a soundboard has collapsed or split, the tone rarely comes back. The second is the glued structure: joints between frame and rims open up in damp conditions, and the first symptom is a closed tone with rattles. The third is playing load: a teaching studio running several classes a day wears an instrument far faster than a household does. The fourth is where it lives — stable humidity between 40% and 60%, out of direct sun and away from radiators, is the cheapest way to add years.
Wear parts are not the end of the instrument. Strings, bridges and tuning pins can all be replaced: new strings when the old set ages, new bridges when the feet deform, a tighten or a swap when a pin slips. None of that is a reason to replace the instrument; the real question is whether it returns to form once the part is changed.
These are the signs that it is time to think about replacing it. A crack that runs through the soundboard, or a visible collapse; joints that have opened and still sound closed after repair; tuning that will not hold for more than a short session; a noticeably worse action, with stiff pressing and uneven string height; or a repair quote close to the price of a comparable new instrument. One of these can be worth fixing — two or more usually is not.
Three places to check on a used instrument. Whether the soundboard shows filler or touched-up finish; whether the seams between soundboard and rims have opened or whitened; and whether the tuning pins turn smoothly or feel slack. These are the most common problems on second-hand guzheng, and the hardest to put right.
For day-to-day care that adds years, see care and tuning; if you have already decided to replace it, the stage-by-stage approach is in the buying guide. For advice on your own situation, leave your contact details and we will answer on the basis of how hard the instrument is worked.