How to thaw a frozen condensate pipe

Every modern condensing boiler produces water as it runs, which drains away through a plastic condensate pipe, usually white or grey and about the width of a finger. Where that pipe runs outside to a drain, it can freeze in a hard frost. The water backs up, the boiler detects it and locks out, and the heating stops, very often on the coldest morning of the week.

It is the single most common winter call-out in the flat, exposed parts of West Norfolk and the Brecks, and in most cases it is something you can fix yourself.

A fault code on the boiler display (the manual will say which), a gurgling sound from the boiler or the pipe, and freezing temperatures outside. Follow the plastic pipe from the bottom of the boiler to where it leaves the house and look for the section outside, especially any bend or the open end over a drain.

Pour warm water, from a watering can or jug, slowly along the outside section of pipe, concentrating on bends and the open end. Warm, not boiling: boiling water can crack the pipe. A hot water bottle or heat pack held against the pipe also works. Do not use a naked flame or a heat gun.

When the ice clears, reset the boiler following the manual. It may take a few minutes to restart. If it locks out again, or you cannot reach or find the pipe, call an engineer.

Lagging the outside section with pipe insulation, enlarging the external pipe to a wider diameter, or rerouting it internally to a waste pipe are all simple, low-cost fixes an engineer can do, often during a service. On an empty property, leaving the heating on a low setting through a freeze also helps.