During these sub zero conditions,many central heating systems are breaking down due to many issues. You can help save your boiler by this easy 'tick over ' tip.
Many heating systems don't have frost prevention but do have a programmable timer with many redundant spaces.
During the night hours, away at work or away, set the timer to heating on at 02.00 switch off at 02.02, on again at 04.00 and off again 04.02 and so on until there is a maximum of 2 hours between all settings. (make sure you don't turn your room thermostat OFF)
This will prevent heat exchanger freezing (common), snow and ice build up around the flue pipe (combustion failure) and also where heating pipes pass through ventilated voids such as lofts and under ground floor spaces, some pipes may not be fully insulated, frost will usually seek them out!
We live in a deep valley where the temperatures plummet, this 'tick over' setting works well for us.