Condensate Pipe Leaking? Here’s Why

If your condensate pipe is leaking, you’re likely experiencing the world’s biggest headache. While I don’t envy you in the slightest, I can offer a slight reprieve – advice. We’re going to talk about what exactly a condensate pipe is, why it might leak, and fixes that you can do from home (when possible). So take a deep breath, remember that this will be over soon, and get reading – we’re here to help.

The most common causes for a condensate pipe leaking are joint leaks, broken heat exchanger, a blocked condensate trap, or a blocked boiler condensate pipe (yes, those are two different things).

Keep reading for a thorough guide on what you need to know to get this dealt with as soon as possible (and hopefully without a professional, if you’re lucky).

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What is a Condensate Pipe?

In short, a condensate pipe is what drains all excess water that condenses in your boiler. You know how water condensates when it’s been heated? Yeah – it does that in your boiler. and to prevent a buildup of that condensation, it’s taken away through a specialised pipe.

The condensate in your boiler is slightly acidic due to the condensed gasses coming off in your boiler. This means that your condensate pipe needs to be made from PVC or ABS pipe, as metal pipes would simply corrode.

If you’re unsure which pipe exactly it is, that’s easy – it’s the only non-metal pipe attached to your boiler.

Troubleshooting a Condensate Pipe Leaking

While it’s common for these pipes to freeze in the winter, it’s also likely that one of the three aforementioned things could have gone wrong. Let’s talk about what those issues exactly entail and how to fix them, shall we?

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Broken Heat Exchanger

This is one of the things that you really want a professional’s eye to look at. If this is the issue, the whole heat exchanger will need to be replaced, and the boiler isn’t the place to start trying your DIY skills out.

The heat exchanger is where your condensate trap and pipes will both meet, meaning it’s a bit of an epicentre of issues if something goes awry. If something has cracked along the way (or the heat exchanger has entirely broken) you’ll notice system and/or mains water leaking into the condensate pipe. This can lead to leaky joints, as PVC isn’t exactly designed to stand up to heat.

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Joint Leaks

For this, you’re going to need to look with your special eyes. Generally, joint leaks occur if the above happens, allowing hot water into the pipe, or there was simply an improper installation. Ideally, you should have PVC pipe cement around each and every joint in the condensate pipe. If you don’t, that’s something you’ll actually be able to fix!

Keep an eye out for:

  1. Any pieces of metal along the condensate pipe. As mentioned above, metal will corrode, meaning it will fail in time. If you notice metal pipes or fittings along your PVC pipe, that’s likely an issue.
  2. Missing or slap-dash PVC pipe cement application. You should see it clearly and purposefully placed around all joints. If it’s fading, cracked, or nonexistent, you’ll need to replace it.

To replace PVC pipe cement, you’ll want to do a few things. First, acquire the cement – it’s at most home and hardware stores for relatively cheap. Next (if your pride can handle it), consult with a gas-safe engineer to ensure you’re doing it right. They’ll often be willing to give advice if it means they don’t need to drive out to help.


  1. Mark your PVC pipe where everything should align. Dry fit your pipe with the connector fitting and mark both to ensure you’re doing so accurately.
  2. Spread the PVC cement along the pipe and fitting, ensuring it’s evenly spread and not too thin.
  3. Align the joint, squeeze them together, and you’re done!

Note: If you aren’t sure if you have the proper fittings – just call a professional to install it. You don’t want to make things worse by accident.

Boiler Condensate Trap Blocked

This is the part that gathers the condensate and discharges it. If you hear a gurgling noise (or something else alarming) coming from your boiler and/or flue, it’s very possible that this trap has been neglected (naughty, naughty). Did you notice that the boiler has gone into ignition lockout after trying to light the burner, it’s a clear sign that this is the issue.

If you’re a visual learner, click here for a video guide on how to clean a condensate trap. Otherwise, keep reading and follow along:

  1. Place a bowl and towel to catch the water that will fall out. Locate your condensate trap (shown in the video above).
  2. Remove the cap and let any water fall out. Remove the entire trap and clean out the bottom hole, removing any debris or buildup that’s occured inside.
  3. Replace the condensate trap and reattach all connections as you found it.

If you’re uncomfortable with this process, call a gas safe engineer. They’ll get this done in a matter of minutes and will spot any other issues that may be present as well.

Boiler Condensate Pipe Blocked

First things first – this is likely going to be difficult for you to pinpoint. That’s okay, but it’s good to know what to look for nonetheless. I recommend hiring a professional to take a look if you suspect this is the issue.

A blocked condensate pipe can occur due to:

  1. Freezing (especially common during winter) condensation inside the pipe.
    1. If you think this is the issue, locate the pipe, put on the kettle, and boil some water. You can pour it down the pipe to clear any frozen blockages.
    2. If you’re unsure how your pipe’s insulation is looking, do not do this. You could severly damage the joints and remaining insulation.
    3. Check for split joints and fittings caused by the expansion due to freezing.
  2. An internal condensate pipe could be blocked by debris and mineral buildup. This will be difficult to troubleshoot, but if you can reach the termination point, you can check one way.
    1. Pour water down the pipe and see if it flows. If it doesn’t, it’s blocked. You may have a pipe that runs into the ground or a soakaway, making this difficult to check without a pro.

Final Thoughts

A leaking condensate pipe is no fun. If you think this may be an issue you’re experiencing, take a look at the above guides. Go through what you can, and then call a professional if the problem persists. You could have a blocked condensate pipe or trap, a leaking joint, or a busted heat exchanger.

While some of these issues can be troubleshot and tested by you at home, others will require a professional eye, depending on your setup. Don’t be afraid to call a gas safe engineer – their job is to help make your life easier.