This Halacha is an excerpt from our Sefer
Buy me here or on Amazon.com
After the blessing, before beginning the Bedika: It is forbidden to talk any words between the blessing and the beginning of the search, just as it is forbidden to make an interval between the blessing and the beginning of the performance of any Mitzvah. This applies even against talking of matters relevant to the search, unless one is in a situation that he cannot begin to do the search without talking [about a certain matter relevant to the search]. If one transgressed and talked after saying the blessing, before starting the search, then if he talked of matters that are relevant to the search, even if one could have begun the search without discussing this matter at that time, nevertheless, the blessing does not need to be repeated. However, if one talked of matters not relevant to the mitzvah, then the blessing needs to be repeated.
After starting the Bedika: Once the search has been started, then one may [even] Lechatchilah talk of matters related to the search. However, regarding unrelated matters, [it is proper] Lechatchilah for one not to talk of them [until after saying the bittul that is said after the Bedika]. This applies even if they involve words of Torah. If, however, one talked of unrelated matters, he is not required to repeat the blessing.
Between the blessing and the start of the search it is forbidden to talk of any matter, even if it relates to the Bedika, unless one cannot begin the Bedika until it is spoken. Once the Bedika has begun, although one may not talk of unrelated matters, it is permitted to talk of matters that relate to the Bedika.
May those helping the father/person perform the Bedika talk during the Bedika?
It is initially proper for them not to talk just as is the law regarding the person himself who said the blessing.
If one went to the bathroom during the Bedika may he say Asher Yatzar?
One may say Asher Yatzar after using the bathroom, before finishing the Bedika.
During the Bedika may one answer Amen and Baruch Hu Uvaruch Shemo after a blessing?
If one hears a blessing during the Bedika, he may answer Amen and Baruch Hu Uvaruch Shemo.
During the Bedika may one recite a blessing upon hearing thunder or seeing lightning?
Walking from house to house and room to room during the Bedika:
Between the blessing and start of the search: Between the blessing and the start of the search, one may not go into another house for the purpose of checking, and he is to first search in the house that the blessing was said in. If one switched houses before beginning the search, then it is considered an interval between the blessing and the Mitzvah and one must thus repeat the blessing. [This, however, only applies if one goes into a different house prior to beginning the search, if however, one simply goes to a different room within the same house, then it does not consist of an interval. Nevertheless, initially one is to begin the search in the same room that the blessing as said in and not switch from room to room.]
After beginning the search: After one begins the search, it does not consist of an interval for one to go into a different house to check for Chametz. [However, Lechatchilah, one should not go into another house which do not need to be checked until the conclusion of the Bedika.]
When checking two separate buildings, such as two different homes, or a home and an office or store, does one say a separate blessing upon checking in the second building?
No. A separate blessing is not recited.
 Admur 432:7
 Siddur; Michaber 432:1 “Tov to…”. However, from Admur ibid it is implied that it is Lechatchilah forbidden to talk of them. Vetzaruch Iyun
 Peri Migadim 432 M”Z 3
Ruling of Admur in Siddur: Vetzaruch Iyun from Siddur who writes “It is proper not to talk of unrelated matters for as long as one is still searching” No mention here is made of the Bittul.
 The reason and other opinions: As there are opinions who say that even one who talks after having begun the mitzvah, its nevertheless considered an interval, and [according to them] one thus needs to repeat the blessing prior to finishing the mitzvah. The reason for this opinion is because this differs from when one talks in the Sukkah during a meal, in which [according to all] one is not required to repeat the blessing of Leishev BaSukkah, [and may even initially talk]. By a Sukkah, the person is not obligated to stay in the Sukkah after having talked, and rather if he wants he can decide to no longer eat and no longer stay in the Sukkah. However, by Bedikas Chametz, being that [when he talks before checking all the areas] he has to continue the Bedika after the talking, being that one is obligated in checking all the areas in which one enters Chametz, and thus for this reason if one would have forgotten to say the blessing before the Bedika, he would have to say it if he did not yet finish the Bedika. Therefore, also now he is obligated to repeat the blessing if he talked after saying the first blessing [prior to finishing the Bedika]. According to this opinion] the same applies for all Mitzvos that are an obligation on a person and he may thus not exempt himself from it [that if he talked in the middle that he must repeat the blessing] [Admur ibid]
Other opinions: The Michaber 432:1 says that the reason that one should not talk is in order so he properly pay attention to the areas that are required to be checked, and thus not forget to check any of the required areas. This follows the opinion of the Rosh in Pesachim that there is no prohibition of making a talking interval after beginning the Bedika, but nevertheless one should not talk so he be able to focus. Admur however does not mention this reason at all, and rather states that talking should be avoided due consisting of an interval.
 Admur ibid
The reason: If one went ahead and talked of unrelated matters before finishing the Bedika, nevertheless, he does not need to repeat the blessing, as [since] he has already begun doing the mitzvah of which the blessing was said on [talking is no longer considered to be an interval, similar to the law by a Sukkah. Thus, bedieved we do not rule like the latter opinion mentioned above, as safek brachos lihakel.] [Admur ibid]
 Implication of Admur 432:8 who rules that lechatchilah they should not enter another room before beginning to check; Piskeiy Teshuvos 432
 Piskeiy Teshuvos 432:1
 Piskeiy Teshuvos 432:1
 Piskeiy Teshuvos 432:1
 Admur 432:8; See Admur 8:22
 Admur 8:22; 432:8 “from house to house”; Ruling of Tosafos and Rav Nissim Gaon that if the rooms are in the same house and one had in mind to do the switch, then it is not considered to be an interval
Background: In 8:22 Admur rules that if one goes from room to room inside the same house after saying the blessing, before doing the mitzvah, then he does not need to say another blessing. Likewise, in 432:8 Admur only mentions that leaving from inside to outside is a problem, and not leaving from room to room. However, Tzaruch Iyun why Admur in 432:7 mentions “After one has begun the search the going from room to room and from house to house to check for Chametz is not considered an interval to require one to repeat the blessing” if he holds that it never constitutes an interval within the same house.
 Ruling of Admur in the Siddur: In the Siddur, Admur writes that “… and they should be careful to first check [the room that they are in or] the room near the room in which they heard the blessing and not go right away and check another room” thus implying that one may only first check in rooms near the room of the blessing, and not in other rooms in the house, as even going from room to room constitutes an interval before one has begun the Bedika. This seemingly follows the ruling of the Ran that it is always considered an interval, even if the person had intention to switch rooms. [See Miluim of Rav Raskin in back of Siddur] Vetzaruch Iyun if one can make such an inference from the Siddur as neither the Shaar Hakolel, Ketzos Hashulchan in Piskeiy Hassidur, or Rebbe in his commentary on the Haggadah mention any difference of the ruling in the Siddur versus that of the Shulchan Aruch, and on the contrary, state it is the same ruling.
 Admur 432:7
 The reason: After one has begun the search the going from room to room and from house to house to check for Chametz is not considered an interval to require one to repeat the blessing, just like when one talks after having already begun a mitzvah is not considered to have made an interval. [Admur ibid]
 This follows the same ruling that Lechatchilah one should not talk of unrelated matters during the Bedika.
 Admur 432:8; Michaber 432:2; M”B 432:7 in name of Maamar Mordechai and Chok Yosef; Kaf Hachayim 432:22
It is evident from Admur ibid that only one blessing needs to be said whether he checks his house and then his store or his store and then his house, as Bedieved we do not consider changing houses in middle of the bedika to be an interval. [Kaf Hachaim 432:22 based on Admur] Likewise, the Michaber explicitly rules that “With one blessing one may search many houses”.
Other opinions: Some Poskim rule that another blessing is to be said before performing the Bedika of a store which is a building separate than one’s house. [Chayeh Adam brought in M”B ibid] Seemingly, his reasoning is because it is considered two separate Mitzvos. The M”B ibid negates this opinion of the Chayeh Adam.