An isha was getting ready to be madlik neiros on yom tov from a pre-existing flame, and her minhag is to make the bracho before she lights. After she made the bracho, the flame she was using went out, and she cried out, “Oh, no!” Is this a hefsek that requires her to repeat the bracho? Now she has to go to the kitchen to get a new flame, and she said “Oh, No,” so should she repeat the bracho?
She does not have to make another bracha, the reason being since it was all part of lighting the neiros.
Although the hefsek was not a need of the hadloka, nevertheless it is related to the mitzvah, therefore b’dieved she would not make another bracha.
O:CH 167-6, M:B 37, Saarei Habracha 13-12 ftnt. 31, Consultation with R’ Stizberg shlit”a, author of Sharei Habracha. Although regarding birkas hamitzvos, the cases that are brought are a need of the mitzvah, nevertheless b’dieved in this case, it wouldn’t be considered a hefsek.