Quality, Honesty & Safety

De-Frosting your Condense Pipe

Condense Pipes QHS

This is part of a series of How-to-Guides put together by QHS to help the residents we serve, on behalf of our Clients, carry out basic checks of their heating systems.

These checks may help you to get your heating system and/or your hot water system working again without the need for an engineer to attend.

In part four of this series of "How To Guides", we explain how to de-frost your condense pipe during cold weather.

  • A condense pipe is a thin white pipe that runs from the boiler to the drain outside. It allows any excess water from the boiler to drain away.

    You can find your condense pipe by looking at the outside wall to which the boiler is fixed.

    Here is a condense pipe

    In cold weather, the condense pipe can freeze. The water draining from the boiler will turn to ice, causing a blockage. This causes water to back-up into the boiler. The system will shut down and sometimes the excess water causes a leak as it backs-up back into the pipes.

    If you have a frozen condense pipe, you will find that your pilot light is flashing on and off. You may also find the boiler makes a low rumbling sound as it tries to fire up.

    It is worrying to be without heating and hot water in cold weather. Knowing how to de-frost your condense yourself is a useful skill to have and may save you from having to wait for an engineer.

    If you are unable to de-frost your condense pipe yourself, QHS are happy to help. You can call us on 01494 795000.


  • Follow these steps to de-frost your condense pipe. You will need a kettle, a watering can and/or a hot water bottle.

    1. Turn your boiler and heating system off completely, even if they are not producing heat and hot water
    2. Add 1/4 cold water to the watering can
    3. Boil the kettle and add 3/4 hot water to the watering can. The temperature of the water should be warm, not boiling
    4. Pour the mixed warm water over the condense pipe (DO NOT USE BOILING WATER as this can melt the plastic pipework)
    5. The condense pipe should gradually defrost
    6. Alternatively, you can place a hot water bottle (in its cover) or a moderately warm microwavable heat pad over the pipe until it defrosts
    7. Turn the boiler back on after you have given the pipe enough time to defrost

    If you have followed these steps and your boiler is still not working, call QHS on 01494 795000 (assuming your property is under contract with QHS).

    Always take care with hot water. If you feel unable to de-frost your condense pipe yourself, call QHS on 01494 795000.

    De-frosting a condense pipe using a watering can

  • There are various ways to defrost an internal condense pipe, such as holding a hot water bottle, a moderately heated microwaveable heating pack or warm cloth around the frozen part of the pipe. Another messier option is to pour hot water over the frozen part using a watering can – don't use boiling water as it could cause the plastic pipe to melt, oh and don't forget to put a bucket, washing up bowl or waterproof container underneath to catch the water!

  • If your condensate pipe has become frozen, the boiler's sensors should detect that it has become blocked and prevent the boiler from operating. This is a normal safety precaution to prevent damage to the boiler. Depending on the make and model of your boiler, different fault codes may or may not be displayed.

  • In laymans terms, the condensate pipe plays an important role in removing acidic wastewater from your boiler to the drains outside of your dwelling. When the temperature here in the UK begins to drop, it's common for the contents of the pipe to freeze, which can cause a blockage, which should result in your boiler completely shutting down as a safety feature.


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