Tefillin
Question
How often do I have to check my tefillin?
Answer
Shalom!
Thank you for your question.
There is actually no true obligation for one to (ever!) check one’s tefillin . In fact, there were many great sages who never did so. One who personally prepared his own tefillin , or purchased them from a reliable individual, is only truly required to check them if they are damaged, for example water was poured over them or they were place next to a fire or somewhere very hot, in such a case one shouldn't wear them until they are checked. This is based on the principle of chazaka (presumption), which teaches that once something is established or certified, there is no reason to suspect that its status has changed. In this case, once tefillin are certified as kosher, they are assumed to remain kosher unless there is reason to suggest otherwise.
The Aruch Hashulchan writes, “It is well known that after a few years, the ink peels off the parchments.… Therefore, it seems to me that one is required to periodically check one’s tefillin , and one should be sure to do so.”
Nevertheless, le'halacha, Hagaon Harav Amrom Fried shlit'a writes that since our tefillin are made of such high-quality leather (מבמה גסה), there is no reason to suspect that the ink or tefillin is damaged; therefore, one does not need to ever check them. On the contrary, it is not good to open them since it could cause damage.