In the UK we'd say a product 'has a design flaw' or 'is inherently faulty/flawed,'
ell.stackexchange.com/users/19309/Steve Ives
I don't see that "inherent" is imprecise.
It's derived from the Latin for "sticking to", so it has the meaning of inextricable.
You could use "intrinsic", which carries the connotation of "essentially inside".
Or "innate", which has the meaning of instilled from the beginning, i.e., "from birth".
ell.stackexchange.com/users/20511/deadrat
The word intrinsic describes the inbuilt nature of something.
A flaw from the design would be intrinsic to the product.
It is a part of the product itself, not something added later by wear and tear.
ell.stackexchange.com/users/4376/Chenmunka
The other answers give 'inherent' and 'intrinsic'.
This would usually be used to refer to problems that are an accepted part of the design of the product.
The 640KB limit was an inherent limitation of MS-DOS.
A design defect is a flaw in the design of the product, which prevents the product from functioning in the intended manner.
A manufacturing defect is a flaw in the product that was introduced during the manufacture of said product.
ell.stackexchange.com/users/6870/Taemyr
I think that Flaw, as in a Flawed diamond, describes an inherent problem well in fewer words.
Inherent is a good word to describe the flaw, but you didn't say if the flaw was of design or manufacturing.
If you're attempting to get redress, it's important to distinguish a "manufacturing flaw" (they messed up making it) as opposed to a design flaw (this item was poorly conceived).
The former is much more likely to get immediate redress, but the second at best will cause a new model or version.
If the product is software you can also use the word "bug" to describe any error that occurs.
ell.stackexchange.com/users/20836/Eric Brown - Cal
I think there is a word to describe that a certain problem in a product was cause by a defect that inherently existed in the product from the start as opposed to something that broke during the usage of the product.  Inherent is close, but I think there is some more precise word for it.
Looking for a word that describes an inherent problem in a product
ell.stackexchange.com
<vocabulary>
ell.stackexchange.com/questions/60273
ell.stackexchange.com/users/19608/traveh
Inherent or instrinsic are good words to describe the flaw. You might say a product "has a design flaw" or "is inherently faulty/flawed". If the product is software you can also use the word "bug" to describe any error that occurs. Flaw, intrinsic and inherent work well. For software, bug can be used.
Intrinsic and inherent work well. Flaw works well, as does bug for software.