What is a condensate pipe and how does it work?

You’d be forgiven for not paying much attention to your condensate pipe – unless it starts causing you problems.

However, it’s a key component in the smooth-running of your home heating system, so it’s helpful to understand the basics.

Doing so will help to:

• Ensure your home heating system is efficient
• Keep the system reliable
• Prevent costly issues from developing

Here, we explain what a condensate pipe is and why it’s important. We also troubleshoot some of the issues homeowners can face with this integral part of their home heating system.

What is a condensate pipe?

A condensate pipe is usually a small, white plastic pipe connected to modern condensing boilers.

Its job is to transport condensate (a byproduct that forms as a result of the normal heating process) safely out of your home.

It channels this liquid:

• Out from the back of your boiler
• Down the external wall
• Into your home’s drainage system or soakaway

It could also be a possibility that the condensate pipe directs the liquid into a waste pipe internally. For example, into the sink waste pipe.

How does a condensate pipe work?

A modern condensing boiler is highly efficient, recycling heat from exhaust gases during operation.

During this process, water vapour condenses within the boiler, creating a liquid called condensate, which is mildly acidic.

A condensing boiler:

• Might produce up to 2-3 litres of condensate per hour
• Will release condensate in small increments
• Will typically release around 300ml at a time
• Helps prevent the external condensate pipe from freezing in winter

When the condensate reaches a certain point within the boiler, it flows through the condensate pipe, and safely into the drainage system.

The importance of the condensate pipe…

In essence, a properly functioning condensate pipe ensures proper disposal of the condensate.

It also prevents damage to the system and your property, and keeps your boiler running smoothly and efficiently.

Condensate pipe insulation

With the condensate pipe normally running down the exterior wall, one of the most common problems homeowners face in winter is the condensate freezing and causing a blockage during colder temperatures.

This can trigger your boiler’s safety mechanism to:

• Shut down
• Lock out the boiler
• Leave you with no heating or hot water

Of course, this is far from ideal. If the outside temperatures are cold enough to freeze the condensate pipe, you’re likely to want your heating on! So what can be done?

Fixing a frozen pipe

If you hear a gurgling sound from your boiler or see an error code on its display that relates to a frozen section, try thawing your condensate pipe:

• Carefully pour warm (not boiling) water over the frozen external pipe. Be careful not to soak the walkway underneath as this could cause a slip hazard
• Or, wrap a hot water bottle around the frozen section of the pipe to slowly defrost it

Preventing problems with freezing condensate pipes

To prevent future issues with freezing, boiler condensate pipe insulation such as foam pipe lagging is often the best preventative measure.

Ensuring your condensate pipe is installed at a sufficient gradient to encourage good flow and prevent blockages is also recommended.

Common issues and fixes

Aside from the main issue of frozen condensate pipes in winter, which we’ve covered above, you could encounter blockages or leaking from your condensate pipe.

Condensate pipe leaking

A leaking condensate pipe is normally a sign of a blockage, poor installation, or damage to the pipe.

If you notice any dripping or pooling around the pipe, take a look to see if you can spot any visible damage such as a split or crack.

Blocked condensate pipe

A blockage in your boiler condensate pipe can stop the condensate from draining away and could see it backing up into the boiler.

This could trigger your boiler to shut down to protect it from damage.

Whether you’re experiencing a blockage or a leaking condensate pipe, contact a qualified heating engineer to assess and safely fix the issue.

Regulations and best practice

Now we know what an integral part of your home heating system the boiler condensate pipe is, what else can be done to help prevent future issues?

Some boiler condensate pipe regulations to follow include:

• Pipe material – As liquid is slightly acidic, pipes should be made from corrosion-resistant plastic (PVC or ABS)
• External pipe length – External length should ideally not exceed 3 metres
• Positioning – A slight downward gradient helps the condensate flow – aim for a minimum drop of 44mm per metre
• Boiler condensate pipe size – A 21.5mm minimum diameter is recommended for internal condensate pipes; external ones must be a minimum of 32mm and insulated with Type-O insulation

You’ll only find trades who meet our high standards and pass our quality checks on Checkatrade.

Find a qualified heating engineer near you

Boilers and their components should only ever be worked on by a qualified engineer. Search your postcode to find highly rated, approved heating engineers in your local area.

FAQs

Where should a boiler condensate pipe drain to?

Condensate is mildly acidic and should therefore drain to a safe point such as a household drain or soakaway. It can also connect to an internal wastewater pipe, such as a sink or washing machine waste pipe.

Can you use push-fit on a condensate pipe?

Push-fit connections are sometimes used on a condensate pipe. However, due to the slightly acidic nature of the condensate, you must use fittings compatible with this type of waste.

What happens if the boiler condensate pipe is blocked?

A blocked condensate pipe can force your boiler into a safety lockout mode. This will stop it from working to prevent potential damage. A heating engineer will need to assess the problem.

Why is my boiler condensate pipe constantly dripping?

If your boiler condensate pipe is dripping constantly, it could be due to a problem with the heat exchanger. Never attempt repairs on your boiler; contact a qualified heating engineer instead.