Hi Simon,
I have read your original post. Several times, and the more I look at it, the more it leads me to the conclusion that you would appear, (whether you actually have or not), to have a vested interest in promoting duty and standby boiler gas installations.
You certainly come across as someone who wants to believe that the solution to a general problem of people dying of cold is dual boilers and your emotive language, e.g. 'gun to the head', is, I believe, trying to get us to agree with you.
In a 'past life' I became qualified, essentially, as a literary critic, and while I cannot speak of authorial intent (that went out of fashion in 1967), I can comment with some authority on how what you have written reads and what it suggests, whether or not that was what you meant it to say. I could PM this whole post, but I think this is too important not to say publicly: I agree with you we need to safeguard the vulnerable and I do not know who else may be reading and quoting from this forum so I want this public.
I have explained that I am confused as to why you are writing the way you are, and I have not had explanation. Instead you talk about the 13kW boiler issue. (I'll answer your point about 8kW boilers in detail by private message as that's irrelevant here. In short, no, I didn't know they were still made.)
I have looked at the language and tone of some of your comments and, quite honestly, they read like the sort of advert they use to sell old people water mains insurance, or insurance on a television, insurance on a satellite dish even.
As you say, your original post does not mention what ways to provide temporary services, but it does specify dual boiler installs and asks what people think of them given that they 'may save our lives one day'. This is very leading language in that you are opening with the idea that our lives are at risk if we do not have a backup boiler. Your whole second paragraph, and I'll quote it in full:
We are now living longer, hyperthermia is a big killer when temperatures drop well below freezing, should we be prepared for the instance when our gas boiler fails and we are unable to find a heating engineer to carry out repairs at short notice.
suggests that there is a reasonable likelihood of not finding a heating engineer 'when', not 'if' our gas boiler fails. When someone reads '[w]e are now living longer', something no one will disagree with, followed by 'hypothermia is a big killer', something we won't deny because it's true, though 'a big killer' has more emotional power than 'a significant cause of death in the elderly' would have, it makes them more likely to accept whatever is in the rest of the sentence. This sentence lulls a reader into accepting the end of the sentence because the beginning is so un-deniably factual, yet several people in this thread have commented that being 'unable to find a heating engineer to carry out repairs at short notice' is unlikely.
Also, it's a rhetorical question: a sentence starting 'Should we[...]' could be answered with 'no', but 'we should be prepared' would have the same meaning as 'should we be prepared?' as, after all, no one would say that to plan to have no contingency measure is a good plan.
The talk of electric backup is an alternative offered in frank response to the question posed in your third paragraph '[w]hat do you think?'. For some of us, we don't think dual boilers is a great solution. I would agree with you that a good installer should offer options but, provided the house has good wiring that will take the load (and it's worth considering that the maximum areas that can be served by radials and ring mains are based largely on the historical need for a socket circuit to take the electrical load imposed by using it for space heating), it would not be in a customer's interest to spend an extra, say, £1000 to pay for a second boiler install, plus maintenance, just to save a few pounds for a week or two running on electric.
Fear tactics work and I have used them myself to allow an old man I used to live with to allow me to fit a washing machine in a spare room. I sold the idea that the existing machine had already broken down before, and could again, but if I put a backup in.... The tactic worked perfectly. The work was carried out entirely at my expense and I paid for the backup Miele washing machine and even left it for the family when I moved out. All I (and the whole family) got out of it was peace and quiet when we sat at the kitchen table and I don't feel bad about doing it as they are still happily using that machine. It cost the old man nothing whatsoever - in fact it added to his and his family's quality of life and to the value of his house. But the tactic is open to abuse, and even if the OP hasn't a vested interest, others may use this thread to scare people into an extra boiler install. Now that scares me more than a boiler breakdown.
I quibble on 'when' rather than 'if' the boiler breaks down because while, given an infinite number of boilers, or infinite time, a breakdown is a certainty, it's worth putting it into perspective that, since 1990, breakdown downtime on all the boilers in all the houses I have lived in has been two hours. In fairness, that was a thermocouple that I changed myself, but I do know (and not through being a plumber) a gas fitter who is generally able to get out to emergency callouts same or next day and who would have mended it in that timeframe even though I was not a priority. No doubt there are other gas fitters. I agree modern boilers are inherently less reliable, especially when you see how some cowboys chuck boilers in without a proper flush or sufficient inhibitor, but even a terrible Glow-worm the above-mentioned old man had ran without being so much as serviced for 8 years before it died. If we care about our customers then we'll do the work properly and boilers will last longer.
I really don't think a boiler breakdown is a likely event, or that it is a life-or-death situation provided we have some form of technical or human backup in place. I agree that hypothermia is a life-or death situation, but often it is caused not so much by 'well below freezing' temperatures (-12°C is a typical winter night in the Alps, much less common in the UK) as by cold weather coupled with lack of decent heating or money to run the heating than by an unlikely boiler breakdown at a time of adverse weather. Again, those who can afford a spare boiler can afford good electrical installations and to run heaters.
Unless, of course the actual question is 'how cheaply could we provide duty and standby boiler installations' which is an excellent question and deserving of a new thread in itself. I'll open one for you even.
On the other hand, if the customers are unable to move electric heaters around and have no one who will help them with this, then perhaps we need to rethink our society more than our heating systems. I suppose I'm more concerned about our genuinely vulnerable who can barely afford the cost of repair than those who can afford duty and standby boilers as the latter can always pay for assistance if need be. I know old people worry, but I think our culture promotes it - there are insurance policies foisted on the elderly for satellite dish installations, water mains etc etc, and I feel a service contract with a decent gas fitting firm is insurance enough. Also, the more people are able to 'be prepared', as you put it, the more unusual it is for someone to need help and the less socially acceptable it would be to ask for it.
Of course an old people's home is an exception, but it is also a situation where there are young and capable staff who are being paid to deal with the situation as needs be, but your continued reference to the elderly and '[w]hat we always have to remember is everybody's circumstances are not always the same' suggests you are not talking about schools and hospitals anyway or care institutions - you are really talking about people in domestic settings.
Whether or not you truly do have a vested interest in this, you have certainly written in a way that comes across as an advertisment for dual boiler installations and I really don't understand why. If English isn't your first language and you learned it through reading adverts (or "Installer" magazine) then I get it, otherwise... I'm still confused.
Enough from me on the subject: I've explained where I'm coming from.
