It is working! Hooray for the man!
The heating problem itself turned out to be an easy one – the control knob wasn’t turned properly. I’d thought that yesterday, but every time I tried turning it the pilot went out. I’m unclear on whether this was muppetry on my part or some other problem, but it’s working now. However, he discovered a couple of other problems that require replacement parts, so will be back before long. The ‘overheat stat’ was broken, and this coupled with a leak via a broken valve means the pressure is too high in the rest of the boiler, which unfortunately he can’t release without installing some kind of release system into a pipe, and…I lost it there, but he seems to know what he’s doing.
Eventually the unit will conk out altogether – maybe another two years, he says – but I’m just happy it’s working for the moment. No need for my old-man blanket any more 🙂