Check to see if your condensate pipe runs along the outside of a wall at any point. The condensate pipe is a small, usually white, plastic pipe that comes out of the bottom of your boiler. It carries the ‘condensate’, which is the liquid produced when all the heat has been taken out of the gas that has burned to provide heating and hot water, to a drain.
Usually, the condensate pipe runs from the boiler to a drain under a sink, but in some cases, it may have been routed through the wall and into an external drain. The part of the pipe that is outside is most likely to freeze when temperatures start to plummet.
If your boiler is located in an unheated part of the house, for example in the garage or out-house, you should treat the condensate pipe as if it was outside.