Our boiler stopped working yesterday morning. It wouldn't restart (it was trying to but would go off again).
Due to these freezing temps, the condensation pipe had frozen.
We established this by tapping the condensation pipe outside the house & could hear it was hollow at the top but sounded dense towards the lower part near ground.
We defrosted it by wrapping old clothing around the frozen area & poured boiling water from kettle about 6-8 times (lost count tbh).
During this process we could hear a crunching noise but that was the defrosting process.
We removed the wet clothing wrapping from pipe once it cooled down & tried restarting boiler & it started up!
Sharing this in case it helps someone out there.
BTW make sure you grit/salt area on ground where hot water would have ran off as it will have iced up.