I have a Sime Friendly Format 80E combi boiler in a house I rent out. For
about a year it's been having an occasional problem of cutting out, and
requiring to be manually reignited. An engineer has tried to fix it but
couldn't find the problem, so it was agreed to leave it alone. However,
the problem has got steadily more frequent, to the extent that it was no
longer reasonable to let it go, and the engineer's just been back for
another crack at sorting it out.

However, the tenant has told me that following the visit, he wase unable to
fix the problem; but worse, the hot water will now only heat when the
central heating's on; and the engineer says it looks like "new boiler"
time.

Could anyone advise what the cause of the original problem might be? And
also, what may have occurred to bring about the new issue?

On the one hand, it's quite an old boiler (~15 years?) so to be fair it
isn't overdue for replacement; but on the other hand it's always been very
reliable, and as it's on a service contract I'm naturally suspicious when
I'm told a repair (ie at their cost) isn't possible, and that a new boiler
(at my cost) is needed.

Thanks for any thoughts