In short... yes, it's likely to have an impact. But I would question whether that makes it financially viable to spend £1500-plus on replacing it with a new model.
For most situations, the two factors most likely to give rise to high gas bills with modern boilers are:
- that it's a Combi (no hot-water cylinder)
- that the return water from radiators is still at a high temperature
Both of these factors take the boiler out of condensing mode within a short time after it fires up. So the SEDBUK "A" rating is meaningless because it's then certainly no longer running at 90% efficiency or better.
Simply replacing your existing Alpha Combi boiler with a modern condensing type doesn't alter either of these two predominate factors.
Now if you were asking me a different question:
"What about replacing the Alpha CD28X with a non-Combi condensing boiler, and installing a hot water tank with the option to later add a solar-thermal input?"
then I would be far more likely to say "Go for it!"
And if you then said you'd like to run underfloor-heating as well (instead of radiators), then there's no doubt you would get greater boiler efficiency. UFH has a much lower temperature for return-water to the boiler. This means it could stay in condensing mode.
So in a nutshell, I'd tend to retain your existing Alpha boiler at the moment...
... but give some thought to the medium-term possibility of a hot-water tank and (partial?) UFH because that's where you'll really increase boiler efficiency.
Finally, before anyone else points it out - yes, I know I've mentioned nothing about the differing levels of insulation between the old and new properties. That's another whole subject!
Save energy... recycle electrons!
