I presume from the posts that this guy got in asking genuine question, that you are all gas safe engineers with no work.
As a Corgi engineer, now Gas Safe the guy is right to explore the possibilities, and well you know it. The BBU's are a pain to take out because its not a straight boiler exchange, even though Baxi do a condensing back boiler unit.
In the older 45/2 and similar being flued in the fireplace it means all the pipework is chopped out, as well as the header tanks and the emersion, so a really crap job, and as far as efficiency goes, you and I both know thats ******. How many of you fit TRV's on all radiators?
Yet you know, or should know that a gas condensing boiler SHOULD NOT HAVE TRV'S really as is detracts from the wonderful figures of how efficient it is, and with TRV's the efficiency drops because of the cycling, rendering it no more efficient than a lot of old boilers, and where then if you take into considering the environmental impact of creating a new boiler, the energy used, and the then notional savings its environmentally inefficient. Condensing boilers are designed to condense being more efficient at lower temperatures, but with on-off controls including TRV's a condensing boiler is only marginally more efficient than a non condensing boiler and sometimes less, depending on the system, and the nett costs in terms of building a replacement and replacement costs.
So some of you should really think when questioning that guys motives, and look more at your own commercial motives.
How many of you even know about optimum efficiency of condensing boilers, or about the potential problems that TRV's cause in the efficiency of a condensing boiler, and how many of you ever fit automatic bypass when they are used? Or how many of you fit water softeners if the boiler specs demand it?
Look at yourselves as 'experts' before you condemn a potential customer.
I've seen similar misguided comments to others with Johnson & Starley Warm Air units, and even customers being told they are irrepairable and inefficient, just to get a job installing a new ch unlikely to be as efficient at that particular system they are replacing taking everything into consideration.
The same misguided idiots created the HIP and the EPC, where I've physically had to explain to these 'experts' that mark down warm air units, suggesting the owner could save this that or the other by spending £3,000 on a new gas condensing boiler, when the existing is very efficient.
Some of you seem to do install by numbers, rather than looking at what the customer is asking, and then judging it on its merits, by inspection.