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Winter advice


How to thaw a frozen boiler condensate pipe

The cold winter months is the time we most rely on our boilers to provide our heating and hot water. But as the temperature falls below zero, the condensate pipe on our boilers can become more susceptible to freezing, causing the boiler to shut down.  

Here we explain how to identify frozen condensate pipe symptoms, tell you how to thaw your condensate pipe and how to stop your boiler condensate pipe from freezing in the future. Use our simple guide to get your boiler working again.

What is a condensate pipe?

The condensate pipe is a small, usually white, plastic pipe that comes out of the bottom of your boiler.  directly outside where your boiler is located. The condensate pipe 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.

Where is the condensate pipe?

Usually, the condensate pipe runs from the boiler to a drain under a sink but do check to see if it runs along the outside of a wall at any point. 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.

How to tell if the condensate pipe has frozen

If the condensate pipe has frozen, you may hear gurgling noises coming from your heating system, and the boiler will shut down.  This is a failsafe mechanism to protect the boiler from water going back up the pipe and inside the boiler, causing damage to the electrics etc.

In most cases, the boiler will display an error code. For example, on most Baxi boilers, the error code will be E133 or E28. The display will alternate between E1 and 33.

How to thaw a frozen condensate pipe

It is simple to defrost your condensate pipe and you shouldn’t need to call your heating engineer. Please wrap up warm and take care not to slip on the frozen ground.

  1. Locate the blockage
    This is likely to be where the pipe is most exposed, outside the building and probably at its end or at a bend or dip in the pipe where the condensate could collect and freeze.

  2. Thaw the pipe
    You can use a hot water bottle or a microwaveable heating pack (the sort used for muscular aches and pains) or a cloth soaked in hot water. You can also pour hot, but NOT boiling, water onto the blockage, but remember that the water may freeze on the ground and make it slippery.

  3. Re-set or re-start the boiler
    Once the blockage has cleared, check the boiler operating instructions or the manufacturer’s website for guidance on any action needed to clear the fault code or alarm and re-start the boiler. If it still doesn’t work, you should call a Gas Safe engineer to come and look at it for you.

Watch our video below that will help you thaw your frozen condensate pipe below.

 How to prevent the condensate pipe from freezing again

Once the condensate pipe is thawed and you have successfully restarted your boiler, you can lag the pipe with waterproof and weatherproof lagging to help prevent it re-freezing.

As a temporary measure, it may help to turn the boiler thermostat (not the room thermostat) to maximum and run the boiler in ‘continuous’ mode, turning the room thermostat to 15°C at night.  Turn back to the normal settings once the cold spell is over.

In the longer term, in order to prevent the pipe freezing again, you can ask your Gas Safe registered installer to move the pipe so that it runs internally.  Or, you could ask them fit a wider pipe, lag it to reduce the risk of freezing, install a trace heater along the pipe which warms it slightly when temperatures drop to freezing, or a combination of all of these.

British Standards, Building Regulations and boiler manufacturers’ instructions all provide information and recommendations that can advise your installer on how to run the pipe to reduce the risk of freezing.  The Heating and Hot Water Council (HHIC) has a very useful leaflet that explains the boiler condensate pipe regulations. Read it here.

Condensate pipe installation is also included in the Benchmark checklist that your installer should go through with you when he has completed your boiler installation.

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