The Met Office has forecast cold weather and a risk of snow. As temperatures fall below freezing, your boiler may show the error code E133, E128 or E28. This can be caused by a frozen condensate. You can fix this yourself quite easily and get your boiler working again.

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.


    1. 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.


  1. 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.

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