Ring the manufacturer's, they will tell you that when it comes to replacing a gas fired system with condensing boiler and C.H.e.S.S best practice controls versus green technology that the gas boiler option is far more economical (payback etc) and there is hardly a difference in "carbon pollution" as electricity is still used. Read up on c.o.p ratio's, comparing rads(rads increased anywhere from 30-40%, lower c.o.p ratio) to underfloor heating(higher c.o.p but more costly, plus being higly impractical for alot of u.k properties). Remeber they are taking mcs registration seriously to combat missells. Air pumps have there place, but bare in mind they are not a panacea, they have limits, something to bare in mind when taking some property off of gas at expense. Also hydrogen fuel cell boiler will mostly likely take the hydrogen via a diffuser from natural gas(could even be efficient town gas). Any one with electricity supply only would be very suited to air source heat pumps, providing all criteria is met, eg insulation.