By Charlotte Beugge

Millions of households are being warned to check their external boiler pipes - or risk total heating failure during the coldest weather so far this year.

According to insurer Direct Line, those affected are households with condensing boilers fitted. Since April 2007, it has been a legal requirement that all new boilers fitted are condensing as these are more energy efficient - but they can cost around £2,000.

With a condensing boiler there is an external pipe which drains away the acidic waste liquid from the boiler, called the condensate. If the pipe freezes the condensate cannot drain away, leading to the "backing up" of the liquid, which will cause the boiler to fail and cut out.

Martin Egan, national property claims manager at Direct Line Home Insurance, comments: "With the arctic weather hitting the UK, we are predicting an increase in boiler failures due to condensing drain away pipes freezing."

However, this is an easily-solvable problem as the pipe simply needs insulating with waterproof lagging. If a pipe has frozen then a professional engineer should be called to defrost it - unless the pipe is at ground level when hot water bottles or heat wraps could be tried to defrost the pipe.

Boiler cover is available as a separate policy from a range of companies including energy suppliers, and emergency home cover can be bought as a standalone policy or as add-on to a home insurance policy.

Calling out a heating engineer for a one-off job could cost more than the basic annual boiler cover, particularly at this busy time of year for heating emergencies.