Seconded - my Zen landline went down a few weeks ago, on a Saturday - Zen quickly identified that it was an exchange fault, diverted my landline calls to my mobile and quoted “up to 3 working days” for it to be fixed by OpenReach.
However within 24 hours, ie Sunday, they rang back to say it should be working again and to check it was OK before they removed the divert.
Excellent service again. It isn’t really the number of faults that matters, they’re mostly out of their control anyway I assume, it’s the way they handle them that really matters. No way will I switch back to PlusNet, or any of the other big operators...