As the hydrogen-rich material piles up on the surface of the white dwarf, a shell of hydrogen builds up. The material burns very quickly in a thermonuclear runaway . The nova will increase in luminosity by a factor of 2000 to 50,000, and on very rare occasions as much as a million times. Typical luminosity, however, is about 100,000 times as bright as the Sun. The process repeats itself .
Material is transferred, builds up, goes boom.
The secondary star is believed to be a red giant star. There are about 10 novae per year in our galaxy, we only see 2 or 3 usually. Usually found by amateurs. During the nova explosion, a part of the hydrogen on the surface of the white dwarf is used up in the thermonuclear runaway, a part is ejected, but some is left on the surface. In any case, some material from the previous outburst is left on the surface when the accretion process starts again.