Is Your Boiler Condensate Pipe Leaking? Here’s What To Do!

6 min read
Gas-certified heating engineer who inspects a condensing boiler pipe leak

We all get to a point in our lives where we wish we had the ability to predict the future. And when you are suddenly faced with some sort of damage in your home such as a boiler leak, this desire becomes even bigger. Fixing something that is already broken and causing problems is difficult. But what if we tell you there is a way to tell the future and become a boiler condensate pipe guru who can detect possible damages even before they occur!

Keep reading and learn how to face this issue head-on.

So, if you are someone who:

  • having trouble recently with your condensate pipe;
  • willing to receive tips from the experts out there;
  • wants to receive some know-how about dealing with common reasons for a condensate pipe leaking

What is a condensate pipe?

There’s just one more thing we need to cover before we step into the spooky world of leaking condensate pipes – their purpose.

The condensate pipe is used to drain all the excess water produced from the condensing process in your boiler. Since the water, aka the condensate, is mildly acidic (that’s because it is a by-product of the condensed waste gasses), it needs to be drained through a PVC or ABS pipe. Any metal pipe used would corrode.

That said, we can easily answer the question Where is the condensate pipe on my boiler? – it is the only non-metal pipe you will see coming out of it.

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Common reasons for a condensate pipe leaking

A frozen condensate pipe is the Lord of headaches, but there are some other unexpected problems that can occur. Some of you may have already faced them, others still haven’t. Whatever the case is, you will find the information laid out here highly useful.

The heat exchanger of your boiler is broken

The condensate trap and pipe come straight out of the heat exchanger, which means that if it cracks or pinholes, it will cause system or mains water to drain into the condensate pipe. What may lead to the condensate pipe leaking is if the hot water causes the pipe joints to fail somehow.

Useful tip: The only way to resolve this problem is to change your heat exchanger. We know that this can cost you a lot, so having a professional inspect your heat exchanger regularly will extend its life significantly.

The condensate pipe joints leak

This can happen if the condensate pipe installation was not done correctly, like if:

  • The joints are not properly sealed: no PVC pipe cement was used for that purpose.
  • The incorrect pipe and fittings are used: the only pipes which can be used to drain the condensate are PVC or ABS. As we already mentioned, any other metal pipe would corrode.
  • If the fittings have metal content (like grab-ring), they will erode as well.<

Useful tip: If the problem is missing PVC pipe cement to seal the pipe to the fitting, you can buy it from your local home store and do the following:

  1. First, make alignment marks on the PVC joints where orientation is crucial. You can do that by dry-fitting the pipe with the PVC pipe connector fitting, and making a mark across both.
  2. Once done, you can spread the PVC cement on both the pipe and the fitting.
  3. Align, press them together and then crack open a beer for a job well done!

However, if the incorrect pipe and fittings were used, maybe it would be better to call a professional, rather than turn it into a DIY project.

The boiler condensate trap is blocked

The purpose of the condensate trap is to gather the condensate produced by the boiler and discharge it afterwards. You might be detecting an upcoming blockage if you start hearing a gurgling noise from the boiler. In order to double-check, you can go outside and see if the flue makes strange noises as well. It is very possible that the boiler will go to ignition lockout on its next attempt to light the burner.

Because of what reasons you can end up with blocked condensate trap?With time, debris can start to deposit in the condensate trap. Tiny bits from the heat exchanger may be corroded and can end up in the sump and eventually in the condensate trap. This, in turn, will stop the flow of condensate, which will go back up into the bottom of the heat exchanger afterwards. And this is how you get a blocked condensate trap! 

Useful tip: Cleaning the trap is a fairly quick job and it is very possible to do it yourself, but call a Gas Safe registered expert first to see how it’s done. Just like with the heat exchanger, a condensate trap should be inspected on a regular basis.

The boiler condensate pipe is blocked

Your condensate pipe can get blocked if:

  • Condensate has frozen inside the pipe, which leads to a blockage and therefore you get a leakage upstream. You can simply solve this problem by pouring warm water onto the pipe. After that, inspect it carefully, along with the fittings, because they might split if frozen. Make sure you have proper condensate pipe insulation, so you can avoid this issue happening again.
  • If your condensate pipe installation is internal itcould be checked by pouring water down it to see if it is flowing where it terminates. However, if the condensate pipe terminates directly into a soil pipe or soakaway, it might be difficult to inspect the end of the pipe. In this case, you will need a heating engineer and ultimately a plumber to solve this problem.

Check also:

How to Fix a Broken Pipe Inside a Wall

How to Fix a Leaking Boiler Pipe

How to Make Your Home Safe from Floods


  • Don’t forget that the condensate is mildly acidic.
  • Any wires near the condensate pipe should be properly covered.
  • Manufacturer’s instructions must be referred to when installing boiler condensate discharge pipes.
  • If there is no gravity route available for a condensate pipe, you could get a condensate pump installed.
  • The condensate either has to go into a drain or into its own purpose-built soakaway. This is basically a plastic container filled with limestone chips to neutralise the acidic levels.

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For questions about the services we offer visit our main site or you can always call us at 020 3404 4045

Image source: caifas / Shutterstock

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5 Responses

  1. Brian Hone says:

    Hi, can i connect an extension to the ribbed condensing pipe. I think there are push on with a screw fitting on the other end.

  2. M Checkley says:

    Could the boiler condensate plastic pipe leaking on the joints cause the pressure to drop on the boiler

  3. Darren says:

    I returned from work to find condensate pipe has blown off and the water is every we’re outside . It looks like some kind of pressure build up and it’s exploded why

  4. Dean says:

    Thank you for putting this out there. I agree with your opinion and I hope more people would come to agree with this as well.

  5. Brian Robertson says:

    I have a vaillant eco pro 28 combi boiler which looses pressure daily.The gas safety engineer has replaced the expansion vessel,intermediate heat exchanger and the main heat exchanger and it still looses presure. When I check the condesation drain after 24hrs there is about 1/2 pint of water in the tray I use to drain.Any HELP?

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