Set to your comfort level and leave that temperature on hold. Most people turn the temperature up during, if home, and down at night for sleeping. The down side to this during extreme weather is the boiler won’t circulate hot water while the inside temperature drops. This could lead to pipes freezing during that off cycle.

Second, if you keep your home at 55, I’d recommend going to 60 and keep it at that temperature until the cold snap is over, all day and night.