DIY goes in cycles (piece on radio4 last night about a DIY heyday in the '80s, following the council house sell-offs) and the last one that seems to have encompassed "heavyweight" work like new CH systems or rewiring would have been in the '70s. Since then, many of the guides have all gone a bit Dennis and reckon you need to get someone in instead.
So I'd not expect coverage of systems developed after this date, and that would include unvented systems, to really make it into the DIY guides.
OTOH, Treloar's NVQ plumbing book covers them, and is a good read.