Answered by Shaykh Abu Usamah
More then often I get nosebleeds due to the weather that tend to go on anywhere from 5 to 15 minutes, with a constant blood flow. One day I was fasting and my nose started bleeding, it went for about 10 minutes or so of constant heavy bleeding, I wanted to know if this makes my fast invalid, makrooh, or what? This was not a fast from Ramadhan but a fast of Thursday such as the Prophet (saw) used to suggest…
Al-Salam `alaykum
Nose bleeding does not invalidate the fast – nor does it make it makruh. There is no need to make up a fast in which this occurred.
For a detailed explanation on those things that do break the fast and those that do not, refer to the article below.
The Fiqh of Fasting
http://www.sunnipath.com/resources/Questions/qa00000302.aspx