24 hours is pretty damn quick to be honest.
I've lived in private rental, Army married quarters and now my own home and I've waited longer than a week before now.
24 hours WITH the part is really very good. 24 hours to come out and look then order the part is usual in my experience, then add on a day or 4 or 5 fir the part to arrive.
It's shit it's happened in a cold snap but in reality when your boiler goes it's never a good time.
I'm in my own hone now with a combi boiler. When my boiler broke down kat winter, I'd just come home from a 12 hour shift and had to be back on work 12 hours later. I had no hot water as not even an electric shower here.
I had to wait 3 days fir a repair man to even come and look at it to work put the problem and oarts needed. I'm all O waited 6 days to be up and running.
I bought a fan heater from Argos and wrapped up and lived in 1 room for the week. I showered at work.
Crap and inconvenient but at least you have some guidelines for yournlandlord/HA to abide to. Us home owners have no such guidelines, nor much spare cash to pay for it. Our boiler gets fixed when we find someone available to come out at a price we can afford. In a cold snap boiler repair men/women are as available as rocking horse poo.
Boilers die, usually when you need them the most. It's always crap and always inconvenient. 24 hours is really very fast to get sorted out.