That's exactly what I plan to do when our oil boiler expires. We built a well insulated low energy house six years ago, but retained the one year old oil boiler from our old house. We have a thermal store, supplied by the oil boiler, solar thermal, a log burner burning our own wood, and three immersion rods. We also have a 3.7kw PV system. Apart from the expense, I can't see too many problems, except perhaps finding someone enlightened enough to fit the new kit!