Every time I run the numbers, there’s not a strong case to upgrade
yep, every case is different, it depends how much gas you use, and what you pay for the gas, at the peak of gas prices last winter,my new boiler/cylinder etc would have paid back in 4 or 5 years (even faster without the government price support) . With prices now significantly lower its looking like payback in around 10 years – but I presume prices will continue to drop a bit over the next couple of years, pushing the return on investment past 10 years.
There are other non financial benefits though – like the house now heats up faster than with the old boiler – cant work out why this would be , but it does. Plus a much greater supply of hot water from the much larger hot water cylinder means we’re not constantly waiting for the water to heat up after one shower etc, plus the water heats up much faster due to the fas recovery coil in the unvented tank. Our newer setup seems just more fit for purpose/better than the old one, but again this does depend how unfit for purpose the old setup is. I think ours was very unfit for purpose
Also some people (not really me though) take the view that return on investment is not as important as just reducing your use of fossil fuels.