Thanks for the sensible responses I received, but I can't help noticing a bit of a defensive note in some of the other posts.
I accept that in this case, it's just one of those things and they guy who serviced the boiler is not to blame.
BUT - I am an 'end user' and I don't know or give a stuff what is says in the service manual, I just wanted to get my boiler sorted out before the winter so it wouldn't pack up in midwinter.
It is a bit of a bummer that I took that precaution, only to find that the boiler packed up anyway.
It sounds to me as if I may as well _not_ bother to employ anybody to service my boiler in future, since it is likely to break down at a random time anyway, at which point I get it repaired or replaced as required.
If any of you wants your websites updated for 125 quid an hour, I would be happy to help, but please not thatI dont do weekend callouts, and any code I have written only has a 24 hour warranty.