Reduces the C14=C15 double bond of 4,4-dimethyl-cholesta-8,14,24-trienol to produce 4,4-dimethyl-cholesta-8,24-dienol. Complements the deletion of the Delta(14)-sterol reductase gene ERG24 in yeast. 4,4-dimethyl-5alpha-cholesta-8,24-dien-3beta-ol + NADP(+) = 4,4-dimethyl-5alpha-cholesta-8,14,24-trien-3beta-ol + H(+) + NADPH Steroid biosynthesis; zymosterol biosynthesis; zymosterol from lanosterol. Belongs to the ERG4/ERG24 family.