I recently got this question in the email:
If I take down multiple Mezuzot for checking, do I make a Brocha when replacing them. I will not be placing them on the same door as they were taken down from as they were not marked to ensure this. What happens if one has be replaced due to its being possul?
This issue always comes up when people have their Mezuzah checked. The problem is that the answer is not so simple because there are several issues here, with multiple opinions involved.
Lets first deal with some more simple issues one by one and at the end I will suggest an answer to the emailer's question.
1. Do you have to say a blessing when reaffixing a Mezuzah to the same door after having it checked?
There are several opinions regarding this. Some say that you would say a blessing if the Mezuzah was down for 24 hours others say you say a blessing only if it was down for 30 days. In this case, one should check with their local Rabbi to find out which custom they should observe. In a case where this is not possible, the rule is that we are always conservative about saying a blessing in a case of doubt. Therefore one would refrain from saying a blessing if the Mezuzah was down for less than 30 days.
2. Do you say a blessing when switching a Mezuzah from one door to another?
Yes. Assuming that the new door is obligated in a Mezuzah according to all opinions. That is to say it has an actual door that opens and closes and that doorway leads to a room that has more that 36 square feet and is used as a living space.
3. If the scribe finds something Passul (not kosher) in the Mezuzah and fixes it, do you say a blessing when re-affixing the Mezuzah to the same door?
First see answer to #1 regarding how long the Mezuzah was down. If the Mezuzah was down long enough it will require a new blessing in any case and this question becomes irrelevant.
Let's assume though that you took the Mezuzah down and brought it straight to the sofer and he found something passul, fixed it and now you are ready to put it up on the same day. In this case, you must ask the sofer if the problem that he found was definitely passul according to all opinions or if he was just fixing something to make it better or to make it Kosher according to more opinions. If the sofer says that it was definately passul, you would make a blessing.
Based on all of the above: In a case like the one described in the email the best thing to do would be to take one Mezuzah that you know was not on the front door and affix it to the front door saying a blessing. When you say the blessing, have in mind that it should exempt all of the other Mezuzahs. Then without interrupting, proceed to affix the rest of the Mezuzahs.