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How to thaw a frozen boiler condensate pipe

If your boiler shows an F28 or F29 error code, it indicates that the condensate pipe needs to be thawed.
Frozen window with ice

If you’ve had a new gas boiler installed in the last 15 years, it will most likely be a energy efficent condensing boiler.

In simple terms, the boiler’s heat exchanger has a high efficiency which can capture heat from the water vapour in the exhaust gases. This creates condensation within the heat exchanger, the condensed water vapour (now just water) then leaves the boiler through something called a condensate pipe.

The condensate pipe is usually a white PVC-U pipe, similar to one you may find on a washing machine or sink waste pipe which usually goes outside into a drain. A boiler condensate can be slightly corrosive to certain materials, especially metals. That’s why condensate pipes are usually made of plastic and not metal.

Once the water vapour has been condensed, it turns into water. A condensing boiler, on average, creates around 2 litres of condensate water per hour, and it needs somewhere to go! By having a condensate pipe, the water is safely disposed of with the rest of the waste water, just like a sink or washing machine.

Where to find your boiler condensate pipe

You'll usually find your condensate pipe leaving your home at the nearest outside wall. It usually looks like a small, white pipe starting from the wall, then heading down into a drain or run off system. Condensate pipes can sometimes be connected straight into wastewater flows, such as the waste pipe of a sink

SIGNS TO LOOK OUT FOR

How do I know if my condensate pipe is frozen?

During low temperatures it’s possible for your condensate pipe to freeze if the pipe terminates outside of your property as water is passing through the pipe. If this happens, it is most likely that your boiler will fail to start, meaning no heating or hot water.

  • Error codes:

    The first warning sign that your condensate pipe has frozen may be an error code on your boiler. On Vaillant boilers, you’ll get an F28 or F29 code. This is the same code on all boiler models and types (system, open vent and combi boilers) Error codes on other makes of boiler may vary.

  • No heat or hot water:

    If your boiler fails to provide heat or hot water, and temperatures outside are freezing, the condensate pipe might be blocked with ice.

  • Gurgling or bubbling sounds:

    Listen for unusual gurgling or bubbling sounds coming from the boiler or the condensate pipe area, as this can indicate a frozen pipe.

  • Visual snspection:

    Safely inspect the external pipe for visible signs of ice formation, particularly during cold weather.

Watch our video on how to defrost your frozen condensate pipe:

How to defrost your frozen condensate pipe

1
Check that your condensate pipe has actually frozen
Check that your condensate pipe has actually frozen

For users who have a Vaillant boiler, specific error codes will indicate a blocked pipe. Look for fault codes (F28 or F29) on the boiler’s display screen to identify this. If you have a third-party boiler, different codes may be used, or you may hear a bubbling and gurgling sound coming from your boiler whilst in use. This could be a sign that your condensate pipe has frozen, which will require immediate attention to ensure continued performance. Note that pipes are more likely to freeze if your boiler and heating system have not been in consistent use during a period of freezing temperatures. This often happens when you leave your home for holiday and do not use your boiler, so we advise to keep your boiler active on a schedule timer to avoid pipes freezing.

2
Locate the frozen blockage within the condensate pipe
Locate the frozen blockage within the condensate pipe

The condensate drainage pipe is a plastic pipe, typically grey or white, connected to the bottom of your boiler. It runs through the wall and outside the property for part of its length. Usually your condensate pipe will be frozen on the most exposed external point, which will typically be at the end of the pipe, just below the drain or around the bend where the insulation is at its thinnest. If possible, check the end of the pipe for any signs of frost to confirm it is frozen internally.

3
Thaw your condensate pipe to remove the blockage
Thaw your condensate pipe to remove the blockage

To effectively defrost a condensate pipe, you can simply pour warm water along the affected area of the pipe to dislodge, melt and remove the ice blockage. Use a suitable container - like a watering can or pitcher - and continue the process until either the ice falls from the pipe or until the contents of the pipe are fully drained. Do not to use boiling water from a kettle as this can damage or crack the pipe, causing damage that will be costly to repair and render your boiler non-functioning for the duration. As another option, you can use a hot water bottle placed against the pipe to assist with the process, and you can wrap a blanket around the external pipe to help insulate and prevent the issue from occurring throughout the winter months.

4
Restart your boiler once ice blockage has been removed
Restart your boiler once ice blockage has been removed

You should always check your boiler manual for instructions on how to reset your boiler correctly before undertaking this operation, then you should restart your boiler. You can avoid having to repeat this process in future by insulating your condensate pipe. By insulating your condensate pipe you are reducing the risk of it freezing and blocking again in future. All good DIY stores should sell pipe insulation, this can easily be fitted with little effort.

How to defrost your frozen condensate pipe

1 / 4
1. Check that your condensate pipe has actually frozen 2. Locate the frozen blockage within the condensate pipe 3. Thaw your condensate pipe to remove the blockage 4. Restart your boiler once ice blockage has been removed
Check that your condensate pipe has actually frozen

For users who have a Vaillant boiler, specific error codes will indicate a blocked pipe. Look for fault codes (F28 or F29) on the boiler’s display screen to identify this. If you have a third-party boiler, different codes may be used, or you may hear a bubbling and gurgling sound coming from your boiler whilst in use. This could be a sign that your condensate pipe has frozen, which will require immediate attention to ensure continued performance. Note that pipes are more likely to freeze if your boiler and heating system have not been in consistent use during a period of freezing temperatures. This often happens when you leave your home for holiday and do not use your boiler, so we advise to keep your boiler active on a schedule timer to avoid pipes freezing.

Locate the frozen blockage within the condensate pipe

The condensate drainage pipe is a plastic pipe, typically grey or white, connected to the bottom of your boiler. It runs through the wall and outside the property for part of its length. Usually your condensate pipe will be frozen on the most exposed external point, which will typically be at the end of the pipe, just below the drain or around the bend where the insulation is at its thinnest. If possible, check the end of the pipe for any signs of frost to confirm it is frozen internally.

Thaw your condensate pipe to remove the blockage

To effectively defrost a condensate pipe, you can simply pour warm water along the affected area of the pipe to dislodge, melt and remove the ice blockage. Use a suitable container - like a watering can or pitcher - and continue the process until either the ice falls from the pipe or until the contents of the pipe are fully drained. Do not to use boiling water from a kettle as this can damage or crack the pipe, causing damage that will be costly to repair and render your boiler non-functioning for the duration. As another option, you can use a hot water bottle placed against the pipe to assist with the process, and you can wrap a blanket around the external pipe to help insulate and prevent the issue from occurring throughout the winter months.

Restart your boiler once ice blockage has been removed

You should always check your boiler manual for instructions on how to reset your boiler correctly before undertaking this operation, then you should restart your boiler. You can avoid having to repeat this process in future by insulating your condensate pipe. By insulating your condensate pipe you are reducing the risk of it freezing and blocking again in future. All good DIY stores should sell pipe insulation, this can easily be fitted with little effort.

How to protect your condensate pipe from freezing again.

Once you have successfully thawed out the condensate pipe, you can avoid it happening again by adding insulating. By doing this, you are reducing the risk of it freezing and blocking again in the future. All good DIY stores should sell pipe insulation, sometimes called pipe lagging and this can be easily fitted with little effort.

To insulate your pipes, you should make sure that the water is flowing correctly out of the pipe. Once this is done, you should then measure out the length of the pipe so then you can make sure that you have a sufficient enough amount of insulation. Cut the length you need and fit it around the exposed pipe. For different types of insulation for your condensate pipe, please see further information here.

If your condensate pipe continues to freeze despite precautions, contact a registered gas safe engineer for a thorough examination and assistance with the issue.

Need more advice from an expert?

Contact your local Vaillant Advance Installer

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