That's interesting. I'm not a plumber but wouldn't it be sensible to do a power flush before considering replacing a boiler? My mum called them because the boiler went off and she couldn't start the pilot again. But they arrived with a bill for a deposit and gave here two or three replacement boiler options without any checks on the old boiler.
In an ideal world..... Yes
I consider myself a good installer. I'm not as good at fixing boilers as I am fitting them.
I'm of the opinion that flogging an old nackered horse is unfair to the horse and its hard on my wrists.
So don't spend good money on a boiler that served you well and now needs to retire.
However ...
in the past I've suggested power flushing the old horse first as it can breath new life into a system and the horse if that horse produces some heat, all the better
Heat is not essential but does help for a better powerflush..
It's a no looser (ish) as I would powerflush anyway when installing a new boiler.
It's worked for me and my customers on 2 or 3 times I can think of.
But on the other hand the old boiler needed a new PCB (let's say) and an engineer replaced that PCB and charged £300. Would you then be happy if 3 weeks later the fan gives up and says its had enough.... would you be happy spending another £250? Then there's always the chance of
the gas valve has plans to retire
Would you not feel that £550 is better spent on a boiler with a 10year warranty?
I explain all this to a customer and in the case of an old lady I suggest we bring her children in on the conversation as I don't like anyone thinking I've done them wrong.
I'm in the process now of pricing a shower room conversion for a man in his mid 80s.
Today I'll take a folder with an estimate and computer generated pictures of my ideas for his conversion. I ask him for his sons phone number who lives 200 miles away on a boat. I'll then bring him into the decision making.