I have an unvented Megaflow cylinder which until recently operated in a conventional manner using a system boiler. However, I have had an extension built which I intend to fit underfloor heating in (water-fed), and as a consequence of this I have now discovered that I have to uprate my boiler. Rather than fitting a new system boiler, and because my extension is south-facing, I wondered whether it would be possible (and worthwhile) heating the Megaflow using solar panels and using the pre-heated water from it at mains pressure to supply a combi?