About 11-12 years ago I came back from Montreal late on a Monday night after a 4 day weekend in Montreal and went to jump in the shower when I discovered no water coming from spigot. I immediately knew a pipe had frozen. I did exactly what upbeat said- turned heat to 80 degrees and opened the hatch to my attic crawlspace where all the water pipes are (I live in a ranch style condo built on concrete slab, so there is no basement, and attic crawlspace is the only place to put water pipes).
Within 2 hours the pipe freeze had melted, and water was running from all spigots. The condo association had numerous pipe freeze ups that weekend and hired an engineer to investigate. The engineer determined that the amount of insulation on the water pipes was totally insufficient for a New England winter. So they hired a contractor to add insulation. I am not sure such construction would even be allowed in Montreal, but in New England it's common for ranch condos to have copper water pipes in attic crawlspaces. No place else to put them.
Let the heat escape from your living space into the piped area, that is key!
BTW this episode happened Presidents Day weekend 2004 or 2005 when ironically there was also a cold snap!!!!