When the Frost Gets to the Boiler
Most modern boilers are condensing boilers, and they drain off a small amount of water through a plastic pipe that usually runs outside the house. On an exposed property on the rise, that pipe can freeze in a cold snap. When it does, the water backs up and the boiler shuts itself down — often showing a fault code, sometimes gurgling beforehand. To the household it is a breakdown, but nothing inside the boiler has actually failed.
If that is what we suspect from your description, we will talk you through finding the pipe and thawing it safely with warm water, never boiling. If it turns out not to be the condensate, or the boiler still refuses to run once it has thawed, the visit goes ahead with the likely parts already on board.
Cold weather also brings out faults that were already on their way. A pump that has been labouring all autumn, a fan that has started to sound rough, an expansion vessel that has lost its charge so the pressure keeps sinking — these tend to fail in the first properly cold week, when the boiler is being asked to work hardest.