The 50plus

What to do if you have a frozen boiler condensate pipe

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Modern gas and oil boilers are by statute, condensing to make them more energy efficient. They achieve the increased efficiency by condensing the water vapour in the exhaust gas thus recovering its latent heat of vaporisation.

The condensed vapour is known as condensate. It is a slightly acidic water which typically runs into a drain via a (usually) plastic pipe. In quite large numbers of installations it is run to an outside drain or just an open ended outside pipe.

Note that most modern boilers are condensing, not just combination (combi) boilers.

If there is a sustained period of freezing or below freezing temperatures, particularly when wind chill further reduces the temperature felt by the pipe, then an exposed condensate outlet can freeze. Once the condensate in the pipe backs up the boiler will detect the problem and shut down, often after making a gurgling noise.

If your boiler has shut down and the outside temperature is freezing then checking the condensate pipe is the first step.

Can this problem be fixed by the occupier? In most cases the answer is yes. The most effective way is to poor warm (not boiling) water over the outside condensate pipe to defrost it. Look for the pipe coming from the boiler which is usually plastic and runs ouside to a drain. It usually freezes from the end upward. Do not try and put water in the condensate pipe. Once the pipe has defrosted try and restart the boiler. If the condensate pipe has been frozen for some time you may need to restart the boiler several times before it will fire up, sometimes over a period a few hours.

Can the problem be prevented? In most cases the problem is caused by the exposed nature of the condensate pipe. Occasionally poor installation is also a factor, such as not enough fall or the pipe being run into gutters or other drains which freeze up. To prevent the problem the ideal solution is to run condensate pipes to an internal drain or soil stack. Where this is not possible the existing pipe should be replaced by an insulated condense pipe and where feasible run on a wall which is not northerly and gains sunlight during daylight hours. Protecting the condensate pipe from the elements will also help.

The small print! The 50plus provides this information without representation or warranties of any kind, expressed or implied, about the completeness, accuracy, reliability or suitability with respect to the information or instructions. The reliance you place on the information herein and any actions undertake are at your own risk. Please take care when using hot water. We recommend you do not work at height.