How to fix a frozen condensate pipe

Author: Michael
1st December 2023
6 min read

If you find that your boiler has stopped working after the cold weather has set in, there’s a chance it may be the result of a frozen condensate pipe.  There is no need to panic, as in this article we look at what and where a condensate pipe is, how you can tell if it’s frozen and how to fix it!

disconnecting the frozen condensate pipe


What is a condensate pipe?

Since 1st April 2005, all new gas boilers fitted in the UK have had to be condensing boilers – this means they convert water vapour condensation into heat making them more efficient.  During the condensing process wastewater forms naturally, which needs to be removed.  This water is transferred from the boiler to an external drain via the condensate pipe, this pipe is normally a white plastic pipe below your boiler.

Ideally, the condensate pipe will be connected to your waste internally, for example your kitchen sink, however this isn’t always possible and sometimes it needs to go to the outside, either into a drain pipe or a soak away.

If your condensate pipe runs externally, or the boiler is located somewhere that isn’t heated such as a garage, it’s very likely the condensate will freeze during the winter months which can cause your boiler to stop working.  It feels odd saying this but when you need your boiler most, the cold weather can stop it from working!


How to find your boiler condensate pipe

The condensate pipe is made of plastic, usually white and connects to your boiler.  If it’s connected to an external drain, you will find the condensate pipe exits the property through the closest external wall to the boiler and then runs down at an angle into your drainage system.

The condensate pipe will normally be white in colour both inside and outside, although the condensate pipe colour, size and material may change as it passes to the outside.  An example of this is a white plastic condensate pipe inside the property, but changes to a black cast iron on the outside of the property.


How do you tell if the condensate is frozen?

If you find that you’re without heating and hot water during winter, a frozen condensate may be the cause.  If this is the case, you may hear the boiler making gurgling noises or you may find that the boiler is displaying a fault code which indicates the condensate is blocked.

In both cases, it’s likely that the boiler will shut down – don’t worry though, the boiler does this to protect itself.  If you suspect your boiler condensate is frozen, and if your boiler is displaying a fault code, a simple google search can help confirm the meaning of the fault code.

Most common boiler error codes include:

Worcester Boiler – 227

Ideal Boiler – Flame Failure or L2 Fault

Viessmann Boiler – F4

Glowworm – F28 or F29

Vaillant – F28 or F29

Alpha Boiler – Nothing or E01

Ariston – A77

Baxi – E23, E53,E113 , E119 or E128

Potterton – E113

Vokera – A01

Navien – 110

Ferroli – A01

How to thaw a frozen condensate pipe

Ok, the good news is a frozen condensate can be easy to fix yourself, so you shouldn’t need to contact an engineer.  To clear the frozen blockage, you will need to thaw the condensate pipe.  But how is this done?

  1. Firstly, find the frozen section – it’s likely this will be at the outlet or at a bend and most likely outside.
  2. Using WARM water from your kettle or microwave in a jug or container – pour it along the frozen section of the pipe (please DON’T use boiling water as this can damage the pipe).  See our helpful video on youtube, see here .
  3. When you think that the blockage has been defrosted, try resetting your boiler by following the manufacturer’s instructions to see if the boiler starts and there are no error codes displayed.
  4. Unfortunately clearing frozen condensate in prolonged colder weather can mean the pipe will only freeze again until the weather improves.  If your condensate pipe is prone to freezing, you should contact a gas safe registered engineer to ask for advice on what improvements could be made to limit the risk of your condensate pipe freezing in future.

If you still experience issues, contact a Gas Safe engineer for assistance.


How to prevent a frozen condensate pipe

When it comes to preventing your condensate from freezing again in the future, you have a couple of options.

Your first option is to insulate the condensate pipe with waterproof lagging to prevent it from freezing, however over the years in dealing with 100’s of frozen condensate pipes, no matter how thick the insulation is, or how big the condensate is, the pipe can still freeze.

The second option would be to have the condensate pipe discharged internally to ensure it stays around room temperature – a qualified Gas Safe engineer can advise further on this.


In cold prolonged cold weather what can be done as a short to medium term solution?

Over the years, in really cold weather, we have had to decide on what can be done in order to get a customers’ boiler up and running over the short to medium term.  The step by step guide below can explain what can be done:

Visit 1 – A Celsius engineer would carry out investigation works as to why your condensate pipe is freezing.  A risk assessment would be carried out and if needed, the engineer would disconnect the condensate pipe and place the pipe into a bucket.  This would be explained to the responsible person on site and if authorisation is given, the condensate would be left discharging into a bucket (which will need to be monitored by a responsible person in the property and emptied as and when needed to prevent the bucket overflowing.  This visit would fall under our engineer visit charge, normally covered under a 1-hour visit charge + any materials used. See here for pricing information.

Visit 2 – Once the weather improves, a Celsius engineer would return and reconnect the condensate pipe (this is a separate chargeable engineer visit as per our pricing above, normally covered under a 1-hour visit charge + any materials used).  During the visit, our engineer can offer advice on how best to improve the condensate pipe installation, in order to remove or reduce the risk of the condensate pipe freezing in future, however this is not always possible due to different property types.



If you experience problems with your boiler and believe it to be due to a frozen condensate pipe, we hope that after reading this article you will be able to fix it yourself and get your heating and hot water back on in no time.

If you find that you’re still having issues with your boiler, or you do not feel confident following these instructions, we recommend that you contact a Gas Safe registered engineer for further advice.

If you would like to speak to a member of the Celsius team, just hit the button below to find out how you can get in touch with us.

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