Electrogear, another alternative, you could fit as suggested two combis. Two Intergas Rapid 25kw, which combined with give over 20 litres per minute, give natural CH zoning, one up one downstairs, and can take solar heated hot water, according to Intergas. You also have backup. They will cost around £650 each. A separate solar cylinder can be fitted later. They are within the gas meter limit.
Have one do one bathroom ad one the other, then one shower doe not interfere with the other. Join the combi DHW draw-offs for the backs using check valves. No G3 needed. You are competent so can service your own combis.
The Ferroli Modena 38C delivers 16 litres min. This maybe capable of taking in solar heated hot water, I am pretty sure it can. The 16 litre per minute may be OK for you and then only the Modena is used.
Have one do one bathroom ad one the other, then one shower doe not interfere with the other. Join the combi DHW draw-offs for the backs using check valves. No G3 needed. You are competent so can service your own combis.
The Ferroli Modena 38C delivers 16 litres min. This maybe capable of taking in solar heated hot water, I am pretty sure it can. The 16 litre per minute may be OK for you and then only the Modena is used.